Alexis Sanchez has said he lost confidence under Jose Mourinho at Manchester United because of the former Chelsea and Real Madrid manager's methods.
Sanchez, signed by Mourinho from Arsenal in January 2018, is a doubt for Monday's FA Cup fifth round clash with Chelsea at Stamford Bridge (live on ESPN+ at 2:30 p.m. ET) after being injured in a collision with an assistant referee during last week's 2-0 Champions League defeat against Paris Saint-Germain.
The former Barcelona forward's injury problem is the latest setback to befall him at Old Trafford, with fitness issues and loss of form seeing him score just five goals in 37 appearances for United.
Sanchez also fell out of favour with Mourinho prior to the Portuguese's sacking as manager in December and, while describing him as one of the best coaches in the world, the player has said that life became difficult during the final months of his reign.
"Mourinho is one of the best coaches in the world, in the way that he coaches, how he studies videos, the way he goes about things," Sanchez told the BBC. "But within the group, there was that feeling that you were in the team, then out.
"Sometimes I didn't play, then I did, then I didn't and as a player you lose confidence."
Sanchez is battling to regain his best form for United, with caretaker manager Ole Gunnar Solskjaer claiming recently that he "can't do anything" to help the 30-year-old reproduce his previously high standards.
And Sanchez admits that he should have done more for the club since his arrival 13 months ago.
"I would like to have brought more joy to the club," he said. "Yes, it worries me because I believe in my abilities as a player, I want to show it.
"He [Solskjaer] hasn't spoken to me a great deal about what I have to do on the pitch, but I think I'm an experienced player and I think I know what I need to do and what I shouldn't do.
"I'm a player that, if I'm not in contact with the ball, I lose that spark, and sometimes I want to play in every game. You're in, you're out, and I'm used to playing.
"It's not an excuse because if I go on for 10, 20 minutes, I have to perform because that's what I'm here for, to make a difference."
Meanwhile, Sanchez has revealed the cause of the injury that has left him racing against time to be fit to face Chelsea.
With Jesse Lingard and Anthony Martial both ruled out of the tie due to injury, Sanchez is likely to start if fit.
But that all depends on a knock sustained before he even entered the action as a substitute against PSG.
"The referee's assistant, when we had a counter-attack, came flying down the line, and I had my foot there and he crashed into me. Bang," Sanchez said.
"And I went back to the dugout and I said to [reserve goalkeeper] Sergio Romero: 'I've just been whacked and I'm about to go on.'
"I've got bruising, but that's not an excuse for not being on my game in the way that I normally am."