Maurizio Sarri highlighted the first-half injury suffered by Napoli's left-back Faouzi Ghoulam as a decisive moment in his side's 4-2 Champions League loss at home to Manchester City on Wednesday.
Napoli led 1-0 when Dries Mertens set up Lorenzo Insigne for a fine opening goal at Stadio San Paolo in a meeting between the league leaders from England and Italy in Group F midweek.
But Ghoulam then sustained what appeared to be a serious knee injury later in the first half, the full-back replaced by Christian Maggio, an enforced change Sarri believes was key as Nicolas Otamendi equalised three minutes later.
John Stones, Raheem Sterling and a record-breaking goal for Sergio Aguero ensured City's place in the next round but Sarri felt Napoli pushed Pep Guardiola's side hard again after a similarly thrilling 3-2 loss at the Etihad on matchday three.
"We ran into a great team and caused them huge problems. We were struggling to re-organise after losing Ghoulam and conceded the goal during that period," Sarri told Mediaset Premium.
"I am sad that we conceded on those counter-attacks, as we had the ball, but causing City so many problems is something to be proud of.
"We have a squad that is technically- gifted and keeps the ball well, but consequently we don't have much height or strength on set plays. That's something we will try to work on, but we must also have to just deal with it.
"As often happens, we play against sides that have 24 hours more rest than we do. In my view, we lost momentum with Ghoulam's injury, as it took a while to re-organise and it becomes difficult to win back possession when they press you that high up the field."
Sarri expanded further on the problems he had replacing Ghoulam, with substitute Maggio typically used on the right side of his defence, with Serie A rules allowing a larger choice of substitutes.
"In the Champions League you have a limited bench, so it's difficult to have both a right and left-back," Sarri said. "In these situations, we tend to bring only the right-back, as Elseid Hysaj has been known to play on the left.
"We were hoping that eventuality would only be for a few minutes, not an hour. It's not easy to replace Ghoulam, as right now he is one of the best left-backs in Europe, but we have the options."
Napoli captain Marek Hamsik praised the way his side started the game but bemoaned City's ruthless streak as a key factor as Napoli lost their third game in four Champions League group matches this season to sit six points behind second-placed Shakhtar Donetsk.
"I think it was the best Napoli I remember in the first 30 minutes," Hamsik said. "We played extraordinarily well in the first half an hour.
"Small details proved decisive tonight but Manchester City are a great side and they always managed to punish every mistake we made."
