The Red Devils have been in stuttering form in recent weeks and have recently been held to 2-2 draws by both Burnley and Leicester City.
Manchester United’s two slip-ups have allowed Manchester City to move 15 points clear at the top of the Premier League table as Pep Guardiola’s men have moved even more out of sight at the summer.
The Red Devils will be bound to be linked with a host of players in the coming weeks and days as the January transfer window draws nearer.
And Cascarino believes that Mourinho should make a move to try and sign Sanchez in January, with the Chile international out of contract at the end of this season.
Writing in his column for The Times, Cascarino said: “[Jesse] Lingard’s success is symbolic of why United will finish second, or even third, and Manchester City will cruise to the title.
“Look at Sergio Aguero – he would walk into United’s team and yet he often finds himself on the bench under Pep Guardiola.
“I think United should try to snatch Alexis Sanchez from Arsenal.
“They managed it with Robin van Persie, and Mourinho would be able to offer him assured starts, whereas he might face more competition at City.”
Manchester United return to Premier League action on Saturday when they host Southampton at Old Trafford as they look to get back to winning ways.
The Red Devils still look on course to significantly improve on their sixth placed finish from last season as they bid to try and qualify for the Champions League once again.
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