Mourinho's side hold a seven-point lead in the Premier League, albeit having played more games than the rest of the top four, and will head into the second leg of their Champions League last 16 tie against Galatasaray level at 1-1 following a draw in Turkey.
Ahead of Saturday's domestic game at Aston Villa and Tuesday's return meeting with Galatasaray, Mourinho expressed concern over the make-up of his squad and whether they can compete on two fronts.
"If you ask me can we go all the way in the Champions League and the Premier League, I think it's very difficult," he said.
"Our squad is quite short; two of our players (January signings Nemanja Matic and Mohamed Salah) can't play in the Champions League. Twenty players minus two players is 18. Minus (the injured) Marco van Ginkel is 17.
"I don't think we have a huge squad in terms of numbers and experience to cope.
"To win the Premier League we have to win nine matches and wait for Man City not to win every match. To win the Champions League we have to beat Galatasaray, we have to beat someone in the quarter final, (the) semi-final, (and the) final.
"When I say someone, I mean the best teams in the world so I think both are very difficult but let's go match by match."
Mourinho, who will be without David Luiz and Ashley Cole at Villa Park, also described the table as fake - with City capable of catching Chelsea by winning their three games in hand.
"We don't look at the table because the table is fake," he added.
"If I watch Tottenham against Arsenal and want Tottenham to win does that help? No.
"I think the team is motivated and strong but not because of the table. They know the table is fake.
"We have clear objectives for the next season but if we can do it this season we don't say no. We are very calm, very relaxed and that's important."
