Chelsea can prey on defensive weaknesses

London: Barcelona are vulnerable defensively and I have believed for a long time that Javier Mascherano is the weak link at the back. He is a midfielder playing at centre-half and he is only 5ft 8in (1.72 metres) but Barcelona are such a good team that he has managed to get away with it until now.

When he was at Liverpool, Mascherano was always impulsive and he liked to hunt in a pack when he chased the ball. That remains the case, but you cannot play like that as a centre-half.

Chelsea's goal last week was a case in point. Mascherano's lack of defensive know-how resulted in him virtually holding hands with Carles Puyol before Ramires crossed for Didier Drogba. As a result, Mascherano couldn't adjust his feet quickly enough to get himself back into position and Drogba scored.

He almost gifted Chelsea an opening goal from their first throw-in last week when he failed to deal with Branislav Ivanovic and his presence will not help the Barcelona back four build a sense of assurance. And because of his impulsiveness, Mascherano is the kind of defender that will give away penalties, so Chelsea can have success if they pinpoint him again today.

Barcelona are also vulnerable in the air. This is the key area of weakness which Chelsea must exploit.

If you struggle against pace defensively, you can compensate for that frailty to some degree by defending deeper. But if you are susceptible to aerial crosses or set-pieces, then there is hardly anything you can do to cover those deficiencies. If Pep Guardiola was to restore Gerard Pique to his back four, it would be an improvement because he is a better defender than Mascherano and he stands over 6ft tall.

But Barcelona have had a problem with height at the back even with Pique in the team. This only highlights how good a team they are because they have still been able to dominate European football. Real Madrid's opening goal in their 2-1 victory on Saturday highlighted Barca's aerial frailties and Chelsea can profit in the same manner.

Target

Every corner, free-kick and throw-in that Chelsea get will give them an opportunity to target Barcelona's biggest weakness and, if they are still in the tie in the final 20 minutes, they will know they have the armoury to take advantage.

Positional discipline is crucial for Chelsea. This ties in with the way they must deal with Lionel Messi. It is a basic principle of playing Barcelona, but is easier said than done.

When Jose Mourinho's Inter Milan overcame Barcelona in the 2010 semi-finals, the tactic worked brilliantly, but when Mourinho tried it the following year with Real Madrid, it flunked because Barca scored early.

When Chelsea lose the ball, they must get back into position instantly. They did this last week, but doing it again over 90 minutes in the Nou Camp will be much more difficult, yet it is critical every outfield player gets back into position as quickly as possible. It worked brilliantly last week because I cannot recall any instances when Chelsea were left three on three or four on four at the back.

Tactically, it is in the balance for Roberto Di Matteo. Chelsea cannot go gung-ho in search of the goal that will leave Barca needing to score three, but they cannot sit back. They need to suffocate the space around Lionel Messi. There is no point in deploying a player to man-mark Messi and I do not expect Di Matteo to even contemplate that.

For Chelsea to make it to the final, they will need Didier Drogba and John Terry to perform as well as they did last week. Di Matteo will be praying Drogba overcomes his knee injury. I think Barcelona will score so that means Chelsea will need a goal too and you would have more confidence in their ability to do that with Drogba in the team.

— The Telegraph Group Limited, London 2012