Carlo Ancelotti's side head into Wednesday's first leg at the San Siro sitting pretty at the top of the Barclays Premier League, four points clear of champions Manchester United with 11 games remaining.
But Mourinho believes his former team are far from invincible, having drawn four and lost four of their 27 league matches under Ancelotti.
Chinks in the armour: Inter coach Jose Mourinho (below) believes Chelsea are not as strong as many give them credit for, despite Didier Drogba's two goals against Wolves (above) sending them four points clear at the top of the Premier League
Quoted in several national newspapers, the Portuguese said: 'The Premier League is never easy - every game normally is difficult.
'But when a team is strong, strong, strong, strong, strong, it doesn't lose so many matches, so many points.'
Mourinho, who led Porto to Champions League glory in 2004 and Chelsea to consecutive Premier League titles in 2005 and 2006, is relishing the clash with his old club.
But he is hoping his former players will not take any extra delight in beating his team, should they manage to do so over two legs.
'If a Chelsea player is happier to beat me than to beat another manager I will be very sad,' he said. 'I just don't understand that. I can't think there would be any special pleasure from that.
'Just as if I am happier to beat them than to beat another team, then I think they have a reason to be very unhappy with me.
'We're all professionals. I want to win, they want to win. Somebody will win, somebody will lose - this we know, this we accept. But there should be nothing more.'
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