The Red Devils forward has struggled since his move to Manchester United in a swap deal from Arsenal in January 2018.
Sanchez has only scored three goals in the Premier League since his controversial move to the 20-time English champions under Jose Mourinho.
Ole Gunnar Solskjaer has used the former Arsenal striker sparingly since the Red Devils legend took over the reins from Jose Mourinho back in December.
In fact, the Chile forward featured in just 20 of Manchester United’s 38 games in the Premier League last season.
Sanchez has been linked with a potential move to Serie A giants Inter Milan before the close of the Italian top flight’s transfer window.
Former Manchester United striker Van Persie gave his verdict on Sanchez’s current situation at Old Trafford.
“He doesn’t look happy to me. I can’t properly judge it because I am not working with him but when I see him play I rarely see him smiling,” Van Persie told BT Sport.
“Of course, I get it when you are playing you need to be serious and you want to win but after you score a goal you can smile, because that is the point of football.
“We all play football because we like it and if you like something you should smile. I think in the first couple of months after his move he was happy and he was playing well.
“Mentally he needs to find that happiness again because if you are happy then you are fitter, you want to create and you want to have fun. So I think he should find a way to be happier again.”
Manchester United missed out on the chance to hoist themselves to the top of the Premier League table on Monday night following a 1-1 draw with Wolves.
Paul Pogba missed a second-half penalty after Ruben Neves cancelled out Anthony Martial’s strike in the first half at Molineux.
Manchester United will host Crystal Palace in the Premier League at Old Trafford on Sunday.
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