Ralf Rangnick is confident Manchester United can challenge for major honours once again, but only with the addition of "top-quality players".
The Red Devils have gone a fifth season without any silverware and are almost certain to miss out on a top-four finish in the Premier League.
Sixth-placed United thrashed Brentford 3-0 on Monday, though they remain five points behind Arsenal in the final Champions League spot having played two games more.
And interim manager Rangnick accepts that some big business is required if United are to make the leap and rival the likes of Liverpool and Manchester City.
Rangnick, who will be replaced by Erik ten Hag at the end of the season, told Sky Sports: "It's obvious quite a few players will leave and there is a need for top-quality players.
"I strongly believe that if everyone works together we can bring Man Utd back to where we need to be.
"Other clubs only needed two or three transfer windows to challenge but from now on we need to bring in top-quality players who really help raise the level.
"If this happens then I don't think it should take too long."
Asked if he has yet to speak to incoming boss Ten Hag, who is still employed by Ajax, Rangnick added: "So far we haven't been able to talk.
"Erik's focus is on winning the Dutch league, our focus was on our games."
United snapped a three-game winless run with their victory over Brentford thanks to goals from Bruno Fernandes and Raphael Varane, either side of Cristiano Ronaldo's penalty.
The Red Devils both attempted (710) and completed (646) more passes against the Bees than they have in any other Premier League game this campaign.
Rangnick was pleased with what he saw in his final home match in charge ahead of away matches with Brighton and Hove Albion and Crystal Palace.
"We were in control for most parts," he said. "In possession that was one of our best performances this year. It was the type of performance we wanted to show to our supporters.
"We played with Juan Mata and Nemanja Matic and that gave us some quality in midfield. It was not too easy for Brentford to take the ball away from us.
"In the first half we played too many square and back passes but in general it was a good performance."
United have won 35 points at Old Trafford in the Premier League this season, which is four more than they accrued on home soil last term (31).
The record 20-time English champions have largely struggled for form, though, and can only match their lowest ever Premier League points tally if they win their final two games.
"In the end I'm not happy with the results, especially in the last four or five weeks," Rangnick added. "Until the West Ham game we were still in the race in three competitions.
"We've conceded fewer goals but in the last few weeks performances have not been as good as they should have been. In general we have lacked consistency."
Brentford are the 21st side in a row to lose their first Premier League trip to Old Trafford and boss Thomas Frank had no complaints with his side's first defeat in five matches.
"We played a Manchester United team who played well today, so congratulations to them," he said.
"I think it was a fair loss. We have had a very good season in many ways. We win or learn and today we learned a lot."