Mourinho is now "plotting to offload" Sanchez, who earns £500,000 a week, and "will ship him out of Old Trafford as soon as he finds a buyer," per the report.
Sanchez only moved to Manchester United from Arsenal in January, but he has failed to have the impact expected, scoring just three goals in 23 appearances since joining the club. He has also been guilty of giving the ball away at an astonishing rate:
His lack of impact cost him his place in the squad against West Ham, as Mourinho explained:
The United boss also confronted Sanchez in training on Monday and reprimanded him for his poor performances in front of his team-mates, according to Fox Sports Chile (via Metro).
Manchester United have plenty of attacking options in Romelu Lukaku, Marcus Rashford and Anthony Martial, which means Sanchez may find it difficult to force his way back into the team.
Mourinho is also under pressure at United after a tough start to the season in which the squad was knocked out of the Carabao Cup and lost three of their opening seven Premier League matches.
And staff at Manchester United believe Mourinho could be sacked soon, according to Simon Jones and Max Winters of the Daily Mail.
Sanchez's form is undoubtedly a problem for Mourinho, and it's one of a number of issues he needs to solve if he is to turn things around at Old Trafford.