Darmian managed to make a very good impression after his £12.7million move from Torino over the summer but following a horror show against Arsenal, the Italian international has not been able to reproduce his early season form in recent times.
United legend Irwin has been following Darmian closely and the former full-back feels that the Italian has gone off the boil but has backed him to quickly recoil.
Speaking to the Manchester Evening News, Irwin said: "Darmian came in and started fantastically well and I think when you get used to the Premier League you sometimes go off the boil. As Memphis Depay has as well, you go off the boil a little bit. But they'll come back strong."
Irwin also feels that Darmian has competition for places with the likes of natural wingers Ashley Young and Antonio Valencia capable in the right-back slot but is confident the Italian will rediscover his early-season form.
"Darmian's got competition because Ashley's done unbelievably well there," Irwin added.
"I don't know how Ashley sees himself, whether he's a winger or just glad to play. But he made one recovery tackle at Palace recently when he came on which was unbelievable and he has played very, very well.
"But sometimes a break does you good, you see it's a different culture, a different climate, a different pace of football, so I'm sure Darmian will be in there challenging for a position again."