Ole Gunnar Solskjaer criticised the decision to make Manchester United play four games in eight days, saying it is "physically impossible" and "made by people who have never played football at this level".
United eased into the Europa League final with an 8-5 aggregate win over Roma, but now face a tough run of games over the next week.
They play Aston Villa on Sunday, Leicester on Tuesday and then Liverpool on Thursday, the latter being a rearranged fixture that was postponed due to protests at Old Trafford last weekend.
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"It’s unheard of,” Solskjaer told BT Sport.
It’s made by people who have never played football at this level. It’s physically impossible for the players to do it after being here, doing Sunday, Tuesday, Thursday, is impossible.
"We have not been dealt a good hand but we will have to play it as well as we can. We will need everyone in these games and we will see how everyone is on Sunday morning. It’s a short turnaround but we will have to be ready, that’s just how it is."
After winning the first leg 6-2 at Old Trafford, United could afford a 3-2 defeat in Rome as they comfortably secured their place in the final.
Edinson Cavani scored both goals for United as they set up a meeting with Villarreal, who overcame Arsenal.
"We played one very good half at Old Trafford, which has brought us through," said Solskjaer.
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“Disappointed to lose the game, especially the way we did, but it was always going to be open and could have been 6-6 or 8-6 to them. It was a strange game.
"We kept giving them the ball and losing it in difficult positions, but luckily we have one of the best goalkeepers in the world and a No 9 up front who wants to score goals. Edi and David [De Gea] two top performances from them."
United captain Harry Maguire added: "It’s a great achievement. Obviously we didn’t win tonight so that’s disappointing, but we did the hard work in the first leg and put ourselves in a great position.
"We knew we needed to start the first half well and we were a bit edgy, but we had chances, they had chances, and we got a good result at half-time. Second half we gave them too many chances. We need to improve for the final but it’s a great achievement. Now we have to go there and win it."
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