Sane damaged the anterior cruciate ligament in his right knee last August and was nearing a first-team return before the Premier League season was suspended due to the coronavirus pandemic.
Gundogan said he was sometimes training with Sane, 24, remotely and feels the attacker – who has been linked with a move to Bayern Munich – could be helped by the hiatus.
"We have the same fitness coach in Germany. Some days we do our exercises via FaceTime. It's worked out well so far and we're on it and trying to be very focused," he said, via the club's website.
"For everyone the situation has its good and bad sides. On one hand, Leroy had already trained with the team and he had his comeback in sight, even though he still had a few minor things.
"But he was almost back at playing again. Especially for your psyche, it's important to be able to play again after such a long time.
"On the other hand, he now has a bit more time to figure out those minor problems he still had. The fact that others can't play either is not so bad for him."
Gundogan, whose side were 25 points adrift of leaders Liverpool when play was halted, admitted it was at times tough to get motivated when training alone.
"I have a few things to do and then I'm ready to go," the Germany international said.
"To be honest, it's not so easy to motivate yourself these days every day when you are training. You know, like people who are working from home, you can maybe compare it to that.
"For those people it's also not the same as driving to work every day and then doing their jobs.
"You have to motivate yourself to do things and to do your work. Some days it's harder than others."
Gundogan captained Germany in all five of their matches as they reached the quarter-finals of their home tournament, ultimately suffering a 2-1 extra-time defeat against Spain.
The midfielder was initially handed the captain's armband by Hansi Flick in the absence of the injured Manuel Neuer last year, retaining it under new head coach Julian Nagelsmann despite Neuer's return to fitness.
Gundogan played a total of 82 games for his country, scoring 19 goals including two at major tournaments – versus Japan at the 2022 World Cup and Hungary at this year's Euros.
Amid rampant speculation over his future at club level, the Barcelona man – who has been linked with a return to former club Manchester City – confirmed his international career was over on Monday.
In a statement posted to X, Gundogan wrote: "After a few weeks of reflection, I have come to the conclusion that it is time to end my national team career.
"I look back with great pride on 82 caps for my home country – a number I could never have dreamed of when I made my senior debut in 2011.
"My highlight was clearly the huge honour of being able to lead the team as captain at our home European Championships this summer!
"After all these years, we have finally succeeded in making the nation proud again – the fact that I was able to play a part in this makes me very happy.
"But even before the tournament, I felt a certain tiredness in my body, and also in my head, which made me think, and the games at club level are not getting less.
"I will definitely remain a fan of this national team and very much hope that the upward trend can be continued together, and there is nothing to stop us from being one of the closest title contenders at the 2026 World Cup."
Gundogan recorded one assist at Euro 2024, as well as averaging 32.8 successful passes per 90 minutes, 25.9 of which were in the opposition half.
His international retirement comes amid reports suggesting he will be leaving Barcelona after just one season with the Catalan giants, who he joined on a free transfer in June 2023.
Gundogan is reportedly attracting interest from clubs in Turkiye and Saudi Arabia as well as City, where he won five Premier League titles, two FA Cups, four EFL Cups and the Champions League between 2016 and 2023.
The former Borussia Dortmund midfielder's last domestic appearance for City saw him score twice in last year's FA Cup final victory over Manchester United, with his first goal being the fastest scored in FA Cup final history, coming just 12 seconds after kick-off.
