A 3-1 first-leg defeat to Napoli in the Champions League last 16 made it five games without a win for Andre Villas-Boas' side and left them with a huge task on their hands to avoid elimination from European competition.

They are also languishing fifth in the Barclays Premier League table and must come through a replay with Birmingham if they are to progress in the FA Cup.

And Zola, working as a Sky Sports pundit in Naples, said: "I think they will have to analyse what is going on and to sort it out quickly."

The club's poor run of results and performances have been characterised by defensive struggles, with the Blues failing to keep a single clean sheet in the absence of captain John Terry, who is expected to be sidelined for a further six weeks by a knee problem.

Zola continued: "Especially psychologically, at the moment they are a little too fragile and you cannot afford that, especially at this stage of the season.

"You have to know what you're doing and you have to do it 100% convincingly."