The Chile international thrived under Wengers management at Arsenal before his controversial move to Old Trafford in January.
Sanchez has struggled to recapture the form which marked him out as one of the most potent forwards in the Premier League, scoring just four goals in all competitions.
The 29-year-old led the line in Turin on Wednesday as Jose Mourinhos side looked to bounce back from their defeat against Juventus a fortnight ago, but Wenger believes it will take time before the former Barcelona winger is back to his best.
I believe he has lost confidence, Wenger told beIN Sports. The strength of Alexis Sanchez is to take initiative to dribble and to take people on.
Those are the players who are most vulnerable when they lose confidence their game is based on that and having that feeling to take initiative, he has lost that slowly.
Since the start of the season he had a high level of physical energy but he has lost that as well.
Certainly he is refreshed now because Mourinho left him out for a while.
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