Mats Hummels heaped praise on former team-mate Henrikh Mkhitaryan and said the easiest way to get the best of the Manchester United attacker is by playing him.
Mkhitaryan was a big-money signing from Borussia Dortmund in the off-season but the Armenia captain's first season in England has been difficult, often out-of-favour under United manager Jose Mourinho.
The 27-year-old made only his second start of the Premier League season since September in United's 1-1 draw at Everton on Sunday, having impressed Mourinho with his pace and creativity in the Europa League and EFL Cup.
And Bayern Munich and Germany centre-back Hummels - who played alongside the Armenian at Dortmund - advised Mourinho to believe in Mkhitaryan.
"If you let him play, you will see how good he is. I am 100 per cent sure of this," Hummels told the Daily Mail.
"He is one of the best I have played with. But if you can't play, you can't shine. It's easy! It's really easy!
"I saw part of the game against Feyenoord. I saw part of the game against West Ham. There he was - always good, as he is always when he is on the pitch.
"He played at that level [raises his hands] all of last year."