- Search results for Alexis Sanchez
The 29-year-old Chilean forward, dropped from the squad for Tuesday's 1-0 Champions League win over Swiss outfit Young Boys, suffered the injury in training on Thursday.
Manchester United were without injured forward Romelu Lukaku with Alexis Sanchez taking his place alongside Jesse Lingard and Anthony Martial.
Following the much-needed win against Bournemouth, Mourinho praised Sanchez and spelt out his preferred system, saying he did not need a traditional centre-forward to lead his attack.
Mourinho has clashed with United stars including Paul Pogba, Luke Shaw, Alexis Sanchez and Anthony Martial.
Prolific in four years at Arsenal and three seasons with Barcelona before then, Sanchez has scored just three times in 23 appearances under Mourinho.
Romelu Lukaku opened the scoring in the 27th minute with a simple back-post header from an Alexis Sanchez cross.
Sanchez is the biggest star of Chilean football and the epitome of a rags to riches success story.
United's build-up to the new campaign has been dominated by manager Jose Mourinho's persistent grumbles over the strength of his squad.
Alexis Sanchez on target as Manchester United beat AC Milan in International Champions Cup friendly
Sanchez fired United into the lead with a well-taken goal on 12 minutes before Spanish midfielder Suso equalised for Milan three minutes later.
Alexis Sanchez was a lively presence after missing the 1-1 draw against Club America of Mexico in Phoenix on Thursday because of visa issues.