Sir Alex Ferguson has launched an inquest into Manchester United's campaign and claims his team's "stupid" 4-4 draw with Everton will be to blame if they fail to secure the Premier League title.
United, who boasted an eight-point lead at the top of the table a month ago, head into the penultimate weekend of the campaign with hopes of winning a record 20th crown out of their hands.
Ferguson and his players must beat Swansea at Old Trafford on Sunday and hope fifth-placed Newcastle stop leaders City from winning if United are to lead the table going into the final game.
Failure to win the Premier League will leave United facing the rare prospect of a trophy-less season, and Ferguson has already started an investigation into why his players have tailed off.
United were 4-2 up against Everton when they conceded twice in the final seven minutes to draw 4-4 on April 22. Since then they have lost 1-0 at Manchester City.
"I think the Everton game was the killer for us. It was an absolutely ridiculous performance in the last 10 minutes of the match. Just absolute carelessness," said Ferguson.
"It's alright saying the history of the club is to attack all the time but it was a stupid performance and it's put us on the back-foot, no question about that.
"If we lose the league we'll have to accept it's the Everton game that did it. No doubt about that."
United are looking to bounce back from a 1-0 defeat at City on Monday and are hoping Newcastle can do them a favour.
"That is a tough game, there's no question about that," added Ferguson, when asked about City's trip to Champions League hopefuls Newcastle.
"They know that, everyone knows that. But at the end of the day, we're on the back foot. We're not favourites, that's for sure."
United are without striker Danny Welbeck, who suffered an injury after a challenge with City midfielder Nigel De Jong last Monday.
"I thought it was a bad tackle," said Ferguson. "I didn't think it was a red card and when I saw it again I thought a yellow card was sufficient.
"It put him out of the game because at the time he was looking as if he was going to do something. I couldn't take him off, of course, because I'd used all our substitutes. That was the disappointing thing for us.
"We lost the impact of Danny at that point so it was a bit of a blow to us."
Swansea start the weekend 12th and with a real chance of ending their first Premier League season in the top half of the table.
Nathan Dyer has been one of the Welsh club's stand-out performers and the winger is confident Swansea can give a good account of themselves at Old Trafford.