The Red Devils signed Sanchez in a swap deal from Arsenal in the January transfer window as Henrikh Mkhitaryan headed in the opposite direction.
Sanchez put pen to paper on a big-money contract after the South American opted to move to Manchester United ahead of Manchester City.
However, the 29-year-old has struggled to impress in a Manchester United shirt so far following a disappointing return of one goal in 11 games in all competitions.
Sanchez struggled to have an impact in Manchester United’s 2-1 aggregate loss to La Liga giants Sevilla in the Champions League round of 16.
Former Arsenal defender Keown believes Sanchez needs to go back to basics at Manchester United.
“I have spoken before about how Sanchez was being overindulged at Arsenal,” Keown told the Daily Mail.
“At Manchester United he is just another member of the group and that is clearly affecting him.
“I remember watching training once at Arsenal and Sanchez came in on his day off wanting to train.
“I cannot imagine Jose Mourinho would take too well to that.
“Sanchez has all the tools to succeed at Old Trafford. He just needs to get his head down and simplify his game a little bit.
“He needs to start higher and wider and threaten defenders around the back as Marcus Rashford does, rather than cutting inside.”
Sanchez is the best paid player at Manchester United ahead of club record signing Paul Pogba.
The Red Devils are in second place in the Premier League table but 16 points adrift of runaway leaders Manchester City.
Manchester United will take on Tottenham Hotspur in the FA Cup semi-final at Wembley next month.
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