Andre Villas-Boas admitted last night that Frank Lampard and Ashley Cole had disputed his controversial decision to leave them out the line-up for last night's 3-1 defeat to Napoli in the Champions League knockout round first leg.

The Chelsea manager had to bring on Cole for the injured Jose Bosingwa after 12 minutes last night and also introduced Lampard and Michael Essien, also left out, with 20 minutes remaining. However, he said that Cole had not been judged fit enough to start the game and had omitted Lampard because he preferred Raul Meireles and Ramires as the defensive midfielders to protect his back four.

On his decision to leave out Lampard and Cole, Villas-Boas said: "I had a conversation with Ashley and Frank. As normal, through the players that they are and the experience they have, they felt they could have helped the team. That's perfectly understandable. In the end, Ashley had the opportunity to come on for Bosingwa with his injury, and Lamps later on in the game. Of course, they were disappointed but they were decisions they have to accept and move on."

Having won just four of his last 14 matches in all competitions, Villas-Boas said that any explanation of his decision would be worthless. "It was a technical decision. Whatever explanation I give you, in the end it would be a fantastic explanation if we'd won the game. Any explanation is now useless given the result of the game, so there's no point.

"Regarding the formation, with [Juan] Mata behind the striker, the two sitting midfielders we chose were chosen in the sense that they are two hard working midfielders sitting in front of the defence. That's not to say that Lamps could not do it, for sure he could, but that was the decision we took.

"It was about sitting and covering up for the amount of space the wing-backs of Napoli get. With Ashley, it was a difficult decision taken [on Tuesday]. He had just two days of training with the team. From [today's] training onwards, he will continue to fight for his position as he normally does. It's his position to take, and nothing else."

John Terry's knee surgery means that he could be out for up to six weeks and Villas-Boas said that he could not ignore the vulnerability of his defence. He said: "We have to focus on reorganising this relationship between this back four that we've recently used. I have to agree, firstly, we have to solve these mistakes at the back so that you can profit better from the amount of opportunities you have and the goals you score. We need this concentration right and this efficiency right for sure.

"At the moment, without John, a very important player for the team, we have suffered a lot of goals recently. We had improved a lot at the beginning of January, so we have missed John."

Villas-Boas said that he still believed his team could turn the tie around in the return leg on 14 March. "Being more clinical and more efficient in front of goal was the difference between the teams. Both had the same amount of opportunities in a very open game, but they had that efficiency that we couldn't find."