who is Man. United's greatest challenge for champions league?

I think Liverpool pose a real threat to Manchester United in the race for the champions league. Liverpool has been playing excellent football recently and their form has peaked at just the right time. I expect to watch an exciting encounter in Athens between Manchester United and Liverpool!

I would say Milan.. Italian football may proved to be something which Man Utd may not get used to. Chelsea, I doubt so, because it's a regular thing to play against Chelsea, so i don't think there will be much surprises

Valencia & Chelsea

Well.. i tink AC Milan will be the greatest challenge of all.. Chelsea will be the second.. AC Milan have great players and great tradition to perform well in the champions league.. Great players like Kaka, seedorf, gilardino and inzaghi are hard to contain.. Chelsea on the other hand.. are looking to win the trophy for the first time dunno since when.. and also they are fighting with Man Utd in all competition which i suppose they will have alot of hunger to out play Man Utd in every competition! however.. They will onli met at the finals if they win all the way..

both chelsea and liverpool are the greatest challenge...liverpool beat barcelona so they are powerful now..chelsea are next to man utd in epl and they had won the carlings cup beating arsenal..so this 2 teams are the greatest challenge in the champions league

chelsea,on last game chelsea had show good performance on leg 2, essian goal is the best goal of the game, but essien will not play on semi final leg 1, i don't know how about chelsea vs liverpool

I think its chelsea only...may be milan too...

hmmm i think chelsea is the greatest challenge for man utd in champions...

chelsea i think

I think it will be Chelsea or bayern.