Barcelona, Real Madrid and Manchester United are the biggest threats to Bayern Munich's hopes of European glory, according to Stefan Effenberg.

The 47-year-old featured for the Bavarian giants as they beat Valencia on penalties to lift the UEFA Champions League trophy at San Siro in 2000-01, and he feels his former club are in a good position to replicate the feat when the showpiece event returns to Milan next year.

However, the ex-midfielder has suggested strong competition will come from Barcelona and Real Madrid, while also tipping Manchester United as surprise candidates for the title.

"It is the same story every year: Barcelona and Real Madrid have very strong squads and I think that both of them are serious opponents for Bayern Munich," Effenberg said at the Aspire Academy Global Summit in Berlin.

"I also think that Manchester [United] can play a good role in the Champions League. That is maybe surprising to you because they lost clearly against Arsenal [3-0 in the Premier League on Sunday].

"But there is still a long season ahead."

The three-time Bundesliga champion still considers Bayern to be the top team and, with a seven point advantage after eight top-flight fixtures, he feels another domestic championship is a mere formality.

"Currently, Bayern Munich is the best football team in the world but they are not unbeatable," Effenberg commented.

"I think the championship in Germany is already decided. No other club in Germany has such quality in their squad. It is almost perfect."