Rashford spent nearly two-and-a-half years playing for Mourinho before he was replaced with Ole Gunnar Solskjaer in December 2018.
“It was tough but I think in five or six years’ time you will look back on it and they are the moments that will give you that mental toughness,” Rashford told The Official Manchester Podcast.
“As an all round player I think I have improved a lot and a lot of it was down to the two years I had under Jose. We had our ups and downs, it was a tough period but one that made me a better player.”
Rashford hasn’t kicked a ball for United for three months after suffering a stress fracture in his back in January.
The 22-year-old is still building up his fitness but the coronavirus pandemic and the suspension of football across Europe has presented a chance for Rashford to play a key role during the final part of the season once the Premier League returns.
“I was probably going to go back with the team mid or end of April but that would have been a push because obviously I didn’t want to miss the summer [Euro 2020],” Rashford said.
“I doubt I would have been 100% fit going into that tournament or even finishing off the season but that is what we were aiming for.
“Obviously since then a lot has happened with this virus, so for my body it’s been good to give it its full duration to rest.”