Jose Mourinho joked that Manchester City's substitutes might be good enough to win the Premier League title this season as he said his former clubs Manchester United and Chelsea must focus on finishing in the top four.

The Portuguese, appearing on Sky Sports before his ex-employers went head-to-head at Old Trafford on Sunday afternoon, was asked who can win the title this season and said: "Four, Man City, Tottenham, Liverpool and the Man City 'B' team.

"When I looked at the bench yesterday, the players not involved, I think even the 'B' team could fight for the title."

City, 5-0 winners at West Ham on Saturday, had a substitutes bench including new signing Joao Cancelo, Bernardo Silva, Ilkay Gundogan and Sergio Aguero – who scored after his second-half introduction.

Neither United nor Chelsea boast such strength-in-depth, with questions asked over United's failure to sign a central midfielder or a replacement for striker Romelu Lukaku, while Chelsea were subject to a transfer ban this summer and lost Eden Hazard to Real Madrid.

Frank Lampard takes charge of Chelsea for the first time in the afternoon fixture, but Mourinho does not expect his former player to face the same pressures as several of his predecessors.

"In this moment, with the transfer ban, that releases the pressure," he said. "They have a very good squad of course. I am very curious to see the direction Frank is going to go.

"Today, does (Olivier) Giroud or Tammy Abraham play? If Tammy Abraham plays and Chelsea doesn't win, people can go in the direction of the younger players, they need time, they are not playing to win the Premier League.

"You don't buy players but you buy time."

Though Mourinho said he did not believe United could win the title, he believes it is vital Ole Gunnar Solskjaer's players do not share that view.

"The dressing room must feel they can win the title," he said. "If they don't feel it, they are in trouble, but I think to finish (in the) top four would be a good achievement."

However, Mourinho, sacked in December by United, admitted he did not have that belief himself at the start of last season.

"When I said that second position the previous season was one of my biggest achievements in football I was not having fun with the words," he said. "I just was just telling you what I was feeling.

"I didn't feel last season we did enough in the transfer window to allow us to compete for the first position because though we finished second the distance to first was very considerable.

"So I don't feel this season they can (win) but I hope they feel they can because that will be an important motivational push for them."