Arsenal legend Alan Smith believes Chelsea will need to score at the Nou Camp on Tuesday night if they are to progress to the Champions League final, but cautioned the visitors not to try and match Barcelona's much-heralded attack-force.

Chelsea take a slim advantage into the second leg this evening courtesy of Didier Drogba's goal at Stamford Bridge last week and will hope to inflict a third consecutive defeat on the Catalans, after Pep Guardiola's side lost to Real Madrid at the weekend.

Roberto Di Matteo has yet to finalise his line-up but Drogba, side-lined from Saturday's goalless draw at Arsenal with a knee injury, is expected to start having featured in training on Monday night.

Didier Drogba
Didier Drogba's goal gave Chelsea the advantage in the first leg. REUTERS

And former Arsenal striker Alan Smith believes the Ivorian will play a key role in the hostile atmosphere of the Nou Camp this evening. Chelsea will likely need to score to give themselves a chance of reaching the final and in Drobga, John Terry, Gary Cahill and Branislav Ivanovic, the visitors possess the kind of aerial power their hosts "patently lack".

"Roberto Di Matteo will naturally have discussed with his players the best ways to go about threatening Victor Valdes's goal," Smith told the Telegraph.

"One of them, without doubt, will come from set pieces, an area Real Madrid successfully targeted three days ago. Even if Guardiola reinstates Gerard Pique next to Carles Puyol, as looks likely, Barca cannot quite match up to Chelsea's height.

"The hard part is getting the ball into areas where you can actually exploit that. Again, Chelsea must decide how to go about this task and I would not be surprised to see them frequently bypass a crowded midfield by hitting Drogba early."

This will be Chelsea's sixth Champions League semi-final in nine years but Di Matteo is under no illusions as to the size of the task at hand. Guardiola's side, unbeaten at home in 15 European games, present a formidable obstacle to Roman Abramovich's pursuit of a trophy he so desperately craves.

Di Matteo said: "We do have the qualities within this team. Away from home, as we've seen in the past, you need a bit of luck to be able to do well in a competition like this. But, certainly, we have the quality and the squad at Chelsea."

Alexis Sanchez
Barcelona's Alexis celebrates after scoring against Real Madrid during their Spanish first division match against Real Madrid in Barcelona. REUTERS

Nevertheless, the Blues are unbeaten against the Catalans in seven matches and there has arguably never been a better time to face Guardiola's side. Defeat to Real Madrid on Saturday saw Barcelona all but relinquish their La Liga crown and it also represented the first time they had lost at home since September 2010.

The last time Barcelona slumped to three defeats in a row was during 2003 and they have not lost two consecutive fixtures at the Nou Camp for almost 20 years. The portents are hardly encouraging and Smith observed that the home side would likely plumb for a more direct approach under the gaze of a restless home support.

"Pep Guardiola was criticised by some for leaving Alexis Sánchez out of the starting line-up against Real Madrid," the ex-Arsenal star said. "His team have lined up without an orthodox striker on plenty of occasions in the past and enjoyed success but it caused them problems in the first half of El Clasico.

"It would be a surprise if Guardiola selected the same team again, pinning his hopes on Dani Alves and young Cristian Tello supporting Lionel Messi in the final third. The feeling is that Sanchez will get the nod to provide a focal point for Barca's attacks.

"There is no question that Barca have missed the injured David Villa this season, but Sánchez can step forward to do a valuable job tonight."