Arsenal midfielder Mesut Ozil has faded as the season has gone on and his German compatriot Muller believes it is because he is not used to such an intensive schedule.
The Bundesliga has only recently returned after a month off, during which time Arsenal played eight matches, and Muller has some sympathy with his Premier League conuterparts.
Muller scored Bayern's second in a 2-0 win at Emirates Stadium on Wednesday in the first leg of Bayern's UEFA Champions League last-16 tie with Arsenal.
He said: "It's not easy for Mesut because you have to play so many games - I don't know how many games he has played for Arsenal without having a break.
"In the Bundesliga we have just had a month off.
"In England it's very hard to be a professional footballer.
"You have any more games than we do in Germany. But I hope Mesut has good games for Arsenal because he is a friend of mine and I know how good he can be."
Muller has also suggested that the lack of a winter break in the Premier League is damaging England's chances at major tournaments.
He said: "When England get to World Cups they look a bit tired.
"The body can recover but the head's another story."
Stop moaning and read what he said. Of course he is right, anyone with any sense will realise that England will never compete like other top national teams because we have to play too many games. Get rid of the league cup and have 18 teams in the EPL with a winter break and we will see a much more vibrant England. But the FA will never do this as they are just as corrupt as the rest of them, to them money comes first even though by putting in place might actually increase revenue. As clubs will get higher attendances and clubs won't have to run at a loss playing in the league cup early rounds. The FA Cup is different and the FA has to start giving something to the back to the fans we have a strong premier league and we can have a strong national side too if they wake up.- crow