Jose's Barca insight will be vital

Although Chelsea must score to progress to the quarter-finals of the Champions League, Jose Mourinho will urge his team to be patient and prepare them for a game of cat and mouse.

He knows the perils of a reckless attacking policy. His four years on the Barcelona coaching staff gave him an insight into their style of play and this experience has helped shape his game plan for tonight's finely-poised second leg.

He probably knows as much about Barcelona as any coach in Europe although, worryingly, this knowledge didn't help much in the first leg in the Nou Camp where the Spanish giants had 68 per cent of the possession and 13 shots on target.

Chelsea failed to get a single shot on target and, after Didier Drogba was sent off in the 56th minute, were fortunate not to lose heavily. As it is, they have the chance to overhaul a 2-1 deficit though Mourinho's tactics will be critical. His team has to strike the right balance between attack and defence. With a 1-0 win sufficient to qualify, Chelsea's natural inclination will be to attack one of the best organised defences in the Spanish league. But this will probably favour Barcelona, famed counter attackers away from home in Europe. They have scored in each of their last eight Champions League ties in England.

Mourinho was on the staff when they scored three against Manchester United at Old Trafford and four against Arsenal at Wembley so he knows that Barcelona take a positive attacking attitude into away legs.

He knows all about the creative brilliance of Deco, an influential figure in his Champions League-winning Porto side last season. Difficult to mark in the Nou Camp a fortnight ago, he will test the diligence of Frank Lampard and Claude Makelele. Such is the variety of Barcelona's attacking line up - Xavi, Ludovic Giuly, Samuel Eto'o and Ronaldinho all carry a serious threat - that Chelsea's defensive strategy needs to be in perfect working order.