Jon Brodkin looks at the choice Jose Mourinho must make up front between the strength of Didier Drogba and the class of Hernan Crespo

Didier Drogba and Hernan Crespo may have ended in tandem against Colchester United on Sunday, but hardly in preparation for Barcelona's visit. The bench beckons for one of them this evening and, of all the decisions Jose Mourinho has to make, his selection at centre forward looks one of the most tricky and vital. Chelsea cannot slip up at home if they are to progress from the tough surrounds of the Camp Nou.

As important as counteracting Barcelona's extravagant attacking talent will be exposing their weaknesses at the back. Though it must delight Mourinho to leave opponents guessing whether to prepare for the force of Drogba or the cunning of Crespo, there are surely times when it vexes him to have to choose. A strong case can be made for either.

Drogba has tended to be first choice in Europe, starting four group games to Crespo's one. The Ivorian's return of a solitary goal may not be outstanding, but Barcelona are unlikely to relish facing his strength and aerial threat. The description of Chelsea as a long-ball team can be overstated, but Drogba provides far more of an outlet for that than Crespo, and Mourinho is happy to make it the primary avenue when required.

Drogba was outstanding when Chelsea took a direct approach at home to Bayern Munich last season, contributing enormously even before he got the final goal in a 4-2 win. The possibility of hitting the ball long may appeal to Mourinho against a Barcelona team less accustomed to such tactics than Premiership opponents, especially given conditions underfoot.

"I'd go for Drogba," says the former Chelsea captain Gavin Peacock, "for probably the simple reason that, with the pitch the way it is, I think it would suit Chelsea better. That way they can go a little bit more direct. Obviously they will play when they can, but they have much more of an option of dropping it over the top for Drogba's pace or firing a few long balls up to his head and playing from there, bypassing that midfield area."

When it clicks for Drogba he is a defender's nightmare. Witness his displays in October's 4-1 victory at Liverpool and against Bolton in the second half of the following match when he scored twice as Chelsea came from behind to win 5-1. He can, though, equally look cumbersome, and his return against Colchester after African Cup of Nations duty was ordinary, even if his diversionary run created space for Chelsea's second goal.

"People criticise him because he doesn't quite have the control at times and he misses chances, but he creates a lot because he's so unorthodox," says Peacock. "He creates stuff out of nothing. He gets the balls that no one else will with pure strength and doing the unusual."

Yet Mourinho is unpredictable. Drogba terrorised Philippe Senderos in the Community Shield, but it summed up the manager's willingness to surprise opponents that Crespo then started against Arsenal a fortnight later. Drogba came off the bench to get the winner.

The contrasting styles of the two front men make them useful for such changes. "A player who's become accustomed to dealing with the runs and movement of Crespo has then got to deal with the aerial threat and power of Drogba," says the former Chelsea striker Kerry Dixon. "They're asking a different question."

Crespo may ask questions to which Barcelona have no answer. Frank Rijkaard's defence tends to hold a high line and the Argentinian is a master at breaking offside traps. Dixon would give him the nod.

"I'm a believer in playing the player who's in form in the position," he says. "Didier's been away with the Ivory Coast and had a good tournament, but the fact he's carrying a knee injury and is not at his best leads me to think that, with Crespo getting a few goals, we don't need to carry any player who's not 100 per cent."

Crespo will hope his removal from Sunday's starting line-up was designed just as a breather. Though he is more likely than Drogba to end up on the margins of a game, he is the superior sniffer of chances and his lesser physical threat and aerial ability may not concern Mourinho tonight. When Chelsea raced into a three-goal lead at home to Barcelona last season, Eidur Gudjohnsen led the line.

Drogba was suspended, having been sent off at the Camp Nou. Even if the second caution was considered harsh, he was arguably too hyped that night and missed a fine chance to put his team 2-0 up. Therein lie further factors for Mourinho to consider.