Cristiano Ronaldo is a "goal machine" who will remain competitive until the day he retires, former Italy and Juventus defender Gianluca Zambrotta has told Stats Perform.

Five-time Ballon d'Or winner Ronaldo has reportedly asked to leave Manchester United if an offer is made after just one season back at Old Trafford.

The Portugal international has yet to return to training with United and is not part of their tour of Thailand and Australia, which has been put down to family reasons.

Ronaldo scored a team-leading 24 goals in all competitions last season, but his homecoming did not go to plan as United registered their lowest Premier League points tally.

United endured a fifth successive season without silverware and finished down in sixth, meaning no Champions League football in the 2022-23 campaign.

That is said to be the reason why Ronaldo is seeking a new challenge, and Zambrotta has backed the 37-year-old to continue firing wherever he plies his trade.

"Ronaldo is a player who makes a difference at the moment. We have seen it. The numbers say this," Zambrotta said. 

"Which team can be right for him? I don't know. Definitely a team fighting for the Champions League, a team fighting for many goals.

"Because I am sure that he always wants to be competitive, until he retires. And I still think Ronaldo is a goal machine any team he plays for."

Ronaldo is the Champions League's all-time leading scorer with 140 goals and has won the competition four times with Real Madrid and once with United in his previous spell.

He scored six goals in last season's competition but could not help United further than the last-16 stage, where they were eliminated over two legs by Atletico Madrid.

However, while United endured a dreadful campaign under Ole Gunnar Solskjaer and then Ralf Rangnick, Zambrotta does not feel Ronaldo was to blame.

"Let's say that he also needs team-mates," said Zambrotta, who represented the likes of Juve, Barcelona and Milan, while helping Italy to World Cup glory in 2006. 

"Even when Ronaldo was criticised at Juve, and they weren't able to move forward in the Champions League, he has always made the difference from a numerical point of view. 

"The data, the numbers say this. You can't think of going against the numbers. And then you may like him, or you may not like him – this is another kind of speech.

"But he has always been a player who has always made the difference from that point of view."

Ronaldo is not the only big-name attacker potentially on the move this window, with Robert Lewandowski also eager to move on from Bayern Munich.

Lewandowski scored 50 goals in 46 games in all competitions last season in his second-best scoring campaign across eight years with Bayern, behind the 55 netted in 2019-20.

The prolific striker has less than 12 months to run on his contract and has made no secret of his desire to leave, with Barcelona this week confirming an offer has been tabled.

It could lead to a bitter split between Bayern and Lewandowski but, like with Ronaldo, Zambrotta can understand why the player wants out.

"I have always been used to not judging anyone because I don't know the personal stories and current events of each case," he said. 

"Everyone can find themselves in a certain moment of their life or career in which they need to change because they need new motivations, new stimuli. 

"He needs a change of scenery, to see new faces, to stay in another stadium, to meet new mates. 

"Maybe at that moment, it was perhaps the right one for a player, so it doesn't affect me and most likely [Lewandowski] wants to change the air. That's all."

Juventus must challenge for both the Champions League and Serie A crowns this coming season after recruiting Paul Pogba and Angel Di Maria.

That is according to Juve and Italy great Gianluca Zambrotta, who also told Stats Perform he expects Inter to be a stronger force with Romelu Lukaku back at the club.

Juve confirmed the signing of former Paris Saint-Germain forward Di Maria on Friday, with fellow free agent Pogba also set to join following his departure from Manchester United.

Pogba knows the Turin giants well having already spent four seasons at the Allianz Stadium, winning the Scudetto in each of those and making 178 appearances in total.

Fellow former United player Di Maria is playing in Italy for the first time, meanwhile, with this the Argentina international's sixth different club in as many countries.

And having brought in players boasting plenty of pedigree, Zambrotta says challenging for Serie A alone – after back-to-back fourth-place finishes – will not be enough for Juve.

"Juventus will certainly have to play a different championship because they must return to be competitive not only in Italy but also in Europe," he said. 

"And they have to do that right away and not just a little bit because they cannot think to wait any more."

Pogba and Di Maria join a squad already boasting the likes of January recruit Dusan Vlahovic and winger Federico Chiesa, who is closing in on a return from a long-term lay-off.

That will be a welcome headache for Massimiliano Allegri, while fierce rivals Inter must also find a way to slot Lukaku back into the side following his return on loan from Chelsea.

"Juve could play with Di Maria on one side, Chiesa on the other side and Vlahovic in the middle," said 2006 World Cup winner Zambrotta, who spent seven years with Juve.

"It is clear that it becomes an important attack, very, very technical and very dynamic on the wings. 

"At Inter, Lukaku is a player who [Simone] Inzaghi did not want to leave anyway, then he left but Inter did very well anyway. 

"So he is a player who certainly can be important for Inter and that the coach clearly values, and he will certainly do well paired with Lautaro Martinez. 

"Then there are many attackers who are possibly leaving. Nobody knows who will come out and who will arrive again. But Lukaku and Martinez are already well tested."

Lionel Messi will remain at Barcelona until the end of his career after president Joan Laporta's efforts in revitalising the club.

That is the view of former Barca full-back Gianluca Zambrotta, who believes the Messi transfer saga will be laid to rest once and for all.

It had looked likely Messi would leave, probably for Manchester City, at the start of this campaign but a dispute over the terms of his contract at Camp Nou proved a stumbling block too far.

The Argentina star has since helped Ronald Koeman's side win the Copa del Rey and they remain in the battle for LaLiga, sitting two points behind leaders Atletico Madrid, who they face on Saturday. 

And Zambrotta, who played for the club between 2006 and 2008, feels Barca now represent a more attractive proposition for Messi since Laporta's election as president for a second time in March.

"They won already an important title in Spain and this is already something," the former Italy international told Stats Perform.

"They are in contention for La Liga title. On Saturday there will be the game versus Atletico Madrid, they are just two points down with Real Madrid, so Barcelona are a team that's still up there regardless of any problem.

"They have the chance to win La Liga too, although it will be a fight until the end.

"I see Barcelona as an improved team in recent months. Laporta has brought enthusiasm and made the place a bit more serene with the aim of keeping their most important player, Messi."

Asked if Barca will achieve that aim, he replied: "I guess so, Messi will never leave Barcelona unless in a distant future he will like to go back to Argentina, but I doubt it.

"I think he will stay at Barcelona until the end of his career."