The Chilean was introduced to a crunch Champions League clash at Old Trafford shortly before half-time.
With Jesse Lingard suffering an unfortunate knock, Ole Gunnar Solskjaer put his faith in a proven performer at the highest level to enter the fold and make a difference.
He was, however, to see Sanchez make little impact during a second half showing which saw Presnel Kimpembe and Kylian Mbappe find the target for PSG and Paul Pogba see red for United.
United now have a mountain to climb in a heavyweight last-16 encounter, but may need the South American forward to aid their cause during a return date in France with others nursing injuries.
Neville hopes Sanchez can find some kind of form by then, with the former Red Devils defender telling Radio 5 Live: “There was a 20-minute period in the second half and United didn't touch the ball and Alexis Sanchez definitely didn't.
“He's not the Alexis Sanchez we fell in love with at Arsenal. He needs a 10 or 15-game run in the team without being brought off to build his form.
“Sanchez's form has dipped so much that at the moment you look at subs to come on and make an impact, he's not the one.
“I don't think he's gone, I think he might have to re-adapt his game. I think it's confidence. He needs some love and he's the one Ole has to work on.
“If Anthony Martial and Jesse Lingard are maybe out, Ole Gunnar Solskjaer has to get Sanchez back in to form.”
United, who will definitely be without the suspended Pogba for a return date in Paris, are due at Parc des Princes on March 6.
Neville gives them little chance of turning the tie on its head, with it likely that the hosts will have Edinson Cavani back in their side by then – even if Brazilian superstar Neymar will still be sidelined.
“I don't think Manchester United have any chance in Paris,” added Neville.
“PSG have too much European nous, too much class.
“Even though we didn't see Mbappe at his absolute best, he was still devastating.”
They are also due to visit Arsenal four days after trying to rescue their continental quest against the Ligue 1 champions.