Mourinho happy to welcome back Duff

The tactic is familiar to Mourinho and was well-used by Sir Alex Ferguson in the past: now that a challenge has been laid down, he will wait with interest to hear what Wenger has to say when he speaks today ahead of Arsenal's match with Sparta Prague. The third instalment could come as early as tonight, should Mourinho feel moved to respond after a match against Real Betis in which a Chelsea win could seal their qualification from the Champions' League group stages.

If Wenger had visited Real Betis's Manuel Ruiz de Lopera stadium yesterday evening for a spot of voyeurism, the Arsenal manager would not have required the telescope which Mourinho cited in his now infamous attack to identify a surprise figure training with the Chelsea squad. The blond hair and the strong left foot would have told him that Damien Duff, injured playing for the Republic of Ireland against Cyprus on 8 October, is back from injury three weeks ahead of schedule.

The 26-year-old's return means that Mourinho has his four wingers to chose from when he takes on a side tonight who were eviscerated 4-0 at Stamford Bridge last month but it was his defence to which the Chelsea manager turned his attention yesterday. For the manager who has everything it is, on occasions, difficult to guess where he can see an improvement, but it is in his back four that he called for an improvement.

If you had asked him about his defence one month ago, Mourinho said, then he would have told you they were playing "perfectly". "We were beating records and suddenly in the last month we made a mistake at Everton, the goal against Charlton and two mistakes against Blackburn," he added. "There was a mistake against Bolton. We are conceding too many goals compared with the past. The secret is to improve in different areas but not to lose the things you are strong at."

He praised his "tough guy" Duff for returning from injury too soon which could be interpreted as a reminder to Arjen Robben that his refusal to play the first leg against Barcelona last season because of injury was poorly-received by Mourinho. Since the Irish winger limped out of that game against Cyprus his nation have failed to qualify for the World Cup and he said that the incentive of success in the Champions' League would go some way as a consolation for that.

The Chelsea team that Duff has left behind, he said, was playing better than at any time since he joined the club more than two years ago. "Some people saw the results against Everton and Charlton as a crisis but we didn't see it like that at all," Duff said. "It was only two draws and we showed how we can bounce back with the result on Saturday."

Chelsea are still yet to concede a goal in the Champions' League this season and a win tonight will leave them and Liverpool, should they beat Anderlecht, to decide who wins the group at Stamford Bridge on 6 December. The only hint at his feud with Wenger came when Mourinho thanked Betis for showing his club "respect" - how this dispute plays out will depend on how little respect the Arsenal manager shows Mourinho this afternoon.

Chelsea (probable, 4-1-4-1): Cech; Gallas, Carvalho, Terry, Del Horno; Makelele; Cole, Lampard, Essien, Duff; Drogba.

Real Betis (probable, 4-2-3-1): Doblas; Melli, Gutierrez, Nano, Castellini; Arzu, Rivera; Sanchez, Edu, Munoz; Oliveira.

Referee: A Hamer (Luxembourg).

The Lowdown on... Real Betis

How do they beat you?

A growing injury list is depriving the team of some of its best players but the core of striker Dani, midfielder Edu and veteran goalkeeper Pedro Contraras can provide the solid platform needed to spring a surprise.

How do you beat them?

Having lost all three of their matches, conceding 10 goals in three games, since Chelsea beat them, Betis have entered free-fall. The team lie fourth bottom in La Liga and defender Miguel Angel Lozano and midfielder Marco Assuncao have joined a growing injury list. Their sluggish starts in games has put them on the back foot too often.

Key man?

Joaquin. Dazzling footwork and lightning pace makes this right-winger a threat to Chelsea's always strong defence.