Manchester City midfielder Ilkay Gundogan has backed former Borussia Dortmund teammate Henrikh Mkhitaryan to have a "big impact" at Manchester United.

The 27-year-old Mkhitaryan is set to make a move to Old Trafford in the coming days after spending three seasons at the Bundesliga club. And Gundogan says, while it may take some time, the Armenia international will become a key figure for Jose Mourinho's side.

"Henrikh has been at Dortmund for three years. The first two years were not so easy for him, to be honest," Gundogan told the Manchester Evening News.

Henrikh Mkhitaryan spent three seasons at Borussia Dortmund after joining from Shakhtar Donetsk. Matthias Hangst/Bongarts/Getty Images

"He's a player who needs self-confidence, who needs to play every time and prove himself to get better and better. At this time, we were not so successful, so it was not easy for him to adapt. He had a few problems.

"But when you see how he played last year, it was really incredible. Maybe he was the most important player for us last year.

"If he can go on like this, he will have a big, big impact for Manchester United, and a big plus. I wish him the best, and to stay healthy."