Sanches joined the Bundesliga champions from Benfica for an initial £27.5millon last summer.
The 19-year-old has only made nine league starts for the German club, and he is yet to score for Carlo Ancelotti's side.
Manchester United tried to sign the midfielder before he eventually decided to join Bayern.
Jose Mourinho claim Renato Sanches was wrong to join Bayern Munich
And now Mourinho claims the Portugal international was wrong to join Bayern.
"There is a Portuguese kid, Renato Sanches, who is a European champion. But he doesn’t play in Bayern Munich," Mourinho said.
"The last match he played, they lost to Hoffenheim.
"Will he play in the Champions League quarter-finals? I have my doubts. You know, there are contradictions in all of us.
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"We want the young boys to play and to perform.
"At the same time, the best teams want to win and it is difficult to win with the learning curve of the young boys.
"You go to other clubs where young players are being developed. It’s easy when there is no pressure playing in mid-table where you can win today, lose tomorrow.
"It’s different at big clubs."