Former Manchester United striker Ole Gunnar Solskjaer said it is undignified of the club to be talking about a fourth-place finish rather than winning the Premier League title.
The Norwegian also admitted that it was hard for him to see Pep Guardiola being appointed as manager of rivals Manchester City and added that United need to "pull themselves together."
Solskjaer, now manager of Molde, famously scored the winning goal for the Red Devils in the 1999 Champions League final and is one of several former players to have spoken out over what is happening at Old Trafford.
The 42-year-old told Olof Lundh's podcast at fotbollskanalen.se: "We are used to winning. We are used to finishing first. We are used to entertaining the fans. If we finished second it was a disappointing season, now the talk is about finishing fourth. It is undignifying for a club like Manchester United."
Solskjaer was supporting United in their Europa League match against FC Midtjylland last week and said before the first leg that there was only a one or two percent chance of an upset.
The Danish team, however, stunned Louis van Gaal's men by winning 2-1 at home in the opening meeting, ahead of Thursday's return game at Old Trafford.
The frustration of Solskjaer was clear in his comments about the team's current style and the decision of Guardiola to join City.
He said: "I am very disappointed in the quality over the past few years. We knew it would be tough after the Ferguson era, but we have not managed to keep the enthusiasm and the entertaining, attacking football.
"It is very tough to see Manchester City managing to get Pep Guardiola and sign the biggest stars in Europe. I am a big fan of Guardiola and his philosophy and all his teams. So now United have to pull themselves together. They are heading for a very difficult time."