The Red Devils won the race to sign Sanchez ahead of defending Premier League champions Manchester City back in the January transfer window.
Sanchez has made an underwhelming start to his Old Trafford career following a poor return of three goals in his opening 18 games under Jose Mourinho.
The Chile international has failed to score in his last five games this season despite having the summer off from international obligations with Arsenal.
Sanchez scored 80 goals in 166 games during three and a half seasons at Arsenal to establish himself as a leading player in the Premier League.
Former Chelsea FC defender Burley believes Sanchez, who didn’t make the bench against West Ham on Saturday, is looking hopeless at the 20-time English champions.
“Sanchez is a bigger problem than Pogba,” Burley told ESPN FC. “Sanchez has lost his way.”
Sanchez won two FA Cup titles during his three and a half seasons at the north London side but the Gunners star struggled to fire Arsenal to the Premier League title.
The Chile international was part of the Manchester United team that lost 1-0 to Chelsea FC at Wembley in the FA Cup final back in May.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news