BAYERN MUNICH coach Pep Guardiola believes Manchester United's absence from Europe this season is a warning to all "big" clubs.

A seventh-place finish in the Barclays Premier League meant the Red Devils are sitting out the Champions League for the first time since 1995 and didn't even qualify for the Europa League.

Ahead of tonight's opening Group E game against Manchester City in Germany, Guardiola was asked about their fallen city rivals.

"It is a good lesson for the big clubs if we think we are unbeatable, that we are so strong," he said. "Every year we need to make the good things happen or next season you could be out.

"That is why football is magnificent.

"The local domestic competition - Premier League or Bundesliga -is the most important because every week you have to be ready."

The former Barcelona boss also hailed tonight's opponents as potential Champions League winners. He said: "City won here in Munich last year with Yaya Toure, Vincent Kompany, David Silva and Edin Dzeko, all fantastic players.

"They are among eight, nine or 10 teams who can win this trophy.

"We would like to be one of those teams."

Bayern will be without Franck Ribery tonight, with fellow winger Arjen Robben also doubtful. The Frenchman, who is recovering from a knee injury, made a brief sub appearance on Saturday.

Guardiola said: "He went to the doctor and he told me he can't play."

Bayern stopper Holger Badstuber tore a thigh muscle tendon at the weekend. He has joined Bastian Schweinsteiger, Thiago Alcantara, Javi Martinez and Rafinha on the sidelines.