Jose Mourinho believes Chelsea will not able to replicate his Inter Milan's treble due to the busy Christmas period.
The Portuguese boss won both the Champions League and the league title at Porto in 2003/04, while in 2009/10 he led Inter to become the first Italian side to win the treble of Serie A, Champions League and Coppa Italia.
After an unbeaten start to the season in all competitions (the Premier League, the Capital One Cup and the Champions League) some have started to claim Chelsea have what it takes to win everything.
But Mourinho is cautious as he believes the busy Christmas period is a huge handicap for English sides against the rest of the European teams.
"First of all, the English teams arrive in the crucial part of the Champions League in difficult conditions," Mourinho said to Chelsea TV.
"The others, they come after a winter break, arriving in the best conditions. The English teams, they arrive after the Christmas period, which is amazing, and for the teams that go further in the domestic cups, it is even more difficult because in January you have a double-legged Capital One Cup semi-final plus two fixtures of the FA Cup. It is very difficult for an English team to do it."
The Portuguese manager has always expressed his preference for the Champions League ahead of winning a domestic league title.
However, he suggests the latter competition will be easier to win.
Mourinho said: "I know the Champions League has more flair; people normally would choose to win it instead of the league and that is a normal feeling. But the cup competitions depend on so many things. They depend on the draws, they depend on details such as at a certain moment you have an important player injured or suspended.
"In the league championship, normally the best team and the best squad win, the squad that is best adapted to give an answer to all the problems. But you cannot choose, you try to improve the team and have the best possible team playing the best possible football, adapted to different situations, and after that it is a case of let's see what is possible to win."
Meanwhile, Mourinho played down the possibility of replicating Arsenal's "invincibles" team - which went unbeaten in the 2003/04 season - after winning ten games and drawing three from the first 13 matches.
"If you play for staying undefeated because that is an objective, maybe you draw so many matches, you don't risk to try to win matches, you are happy just to be undefeated,' Mourinho said.
'If you get 10 draws you get 10 points, and if you win five games and lose five games, you get 15 points. I would prefer 15 points and to lose matches than 10 points and be undefeated."