The Chile international has been a hot property in the transfer market over the past 12 months or so.
Sanchez was allowing his contract to run down amid reported interest from Premier League leaders Manchester City.
The Citizens appeared to be closing in on a deal for Sanchez in the January transfer window at the end of 2017.
However, Manchester United managed to complete a swap deal to sign Sanchez from their bitter title rivals Arsenal.
The South American put pen to paper on a contract believed to be worth around £350,000 a week at Old Trafford.
But Sanchez has only managed to score two goals in 11 games in all competitions to prompt criticism of the Chilean forward.
Former Chelsea FC winger Nevin believes Sanchez is struggling in a diminished role in the Manchester United.
“When you’re not the core player, and at your previous club everything came through you, suddenly you looked a much better player,” Nevin told Irish radio station Newstalk.
“If you go to another club and there are three or four attackers and the game isn’t being played to your style, you’re just as good a player, but it’s not suiting you.”
Sanchez won two FA Cup titles in three seasons at Arsenal but didn’t come close to Premier League title glory.
The South American could win the FA Cup for a third time this season but Manchester United will need to get past Tottenham Hotspur in the last four.
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