Sanchez signed for Manchester United from Arsenal 10 months ago, moving in a direct exchange with Armenia international Henrikh Mkhitaryan.
He has, though, been a massive disappointment since, managing just four goals since that blockbuster move.
Alexis Sanchez was formidable before his Manchester United move, firing Arsenal to two FA Cup triumphs during his time in north London.
The Chile international was also widely regarded as among the best, and most consistent, performers in the top flight.
His struggles at Old Trafford have, therefore, left many fans and pundits baffled.
And Mourinho has now opened up on Sanchez ahead of Manchester United’s Premier League clash with Everton on Sunday (4pm).
“In this moment he’s struggling because he’s injured and we come to the Chelsea match to try to help the team but his physical condition was not good and then he had to stop and was not available for Juventus and is not available for tomorrow again, so now is to be physically in the best conditions,” he said.
“He arrived January, in the first period of the season for him.
“I don’t think is ever an easy situation for a player but this season he had a good start a good pre-season, he started well against Leicester, and then he was injured.
“Then he came back and was injured again and he is the kind of player that needs to be really really sharp.”
Many United fans have been calling for Romelu Lukaku to be dropped.
Sanchez’s injury, however, has seen the Red Devils’ attacking options restricted.
And Mourinho has suggested he cannot afford to drop Lukaku.
“Well against Juventus, I couldn’t give him a break,” he added.
“I don’t think Carrick can play as a striker, so against Juventus we played with the players that we did.
“If we decided to give a rest to Lukaku and play Rashford, then who plays as a winger?
“We are not in the best moment to try to think about resting players or try to find solutions, the solutions is to use the players we have.”