The Chile international completed a move to the Red Devils in a swap deal with Arsenal after Wenger oversaw the signing of Henrikh Mkhitaryan in the January transfer window.
Sanchez established himself as a key member of Wenger’s side during his three and a half seasons at the north London side.
The 29-year-old scored 80 times in 166 games in all competitions to prove that he was one of the leading talents in the Premier League.
However, the South American forward has only found the net with four goals in 27 games since his switch to Manchester United from Arsenal earlier this year.
Sanchez’s only goal in the current campaign came in a 3-2 win over Newcastle United at Old Trafford at the start of October.
The Chile forward lasted 79 minutes in Turin before he was replaced by Juan Mata with 11 minutes to go.
Mata went on to score an equaliser before Alex Sandro’s own goal secured a famous 2-1 comeback win at Juventus in the Champions League.
Sanchez’s former Arsenal manager Wenger believes Sanchez is lacking in confidence in the Manchester United team.
“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.”
Sanchez will be hoping to retain a starting spot in Manchester United’s team for their clash against Premier League leaders Manchester City in the derby at The Etihad on Sunday.
The South American forward spent one season playing under Citizens boss Pep Guardiola at FC Barcelona between 2011 and 2012.
The Red Devils have come from behind to secure 10 points from losing positions in five of their last six games in all competitions.
Manchester United haven’t won the Premier League title since 2013 when Sir Alex Ferguson got his hands on his 13th and final top flight crown.
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