If Napoli want to replace lukaku with potential striker will not take them long time before they will get someone that will fit his wing but Napoli will not embark on such risk, because lukaku is giving the club what they want from the player. Is like you don't know that there are many players in some cluds just that they have not been allow to join club of their choice that will make them shine.
Romelu Lukaku has a serious injury and he will stay out of the fields for months. He will not have a surgery but he cannot return before at least another month if not couple of months.
His team will have to deal with his absence for quite long time so unless they do very well in the first matches, they will be in hurry to find a suitable replacement
A report I read suggested he'll be injured for three months, but I'm not sure, of course. Perhaps that process could be accelerated. Romelu Lukaku is a very important player for Napoli. The player who replaces him should score a lot of goals for Napoli. Lukaku is a key striker who has scored a lot of goals for Napoli. Napoli will miss him in the Italian league.
Lukaku injury is likely to be out for 3-4 months, as Lukaku injury is indeed quite serious. Even if he recovers soon he still needs rest to fully recover and prevent a recurrence. So it's understandable that Napoli is quickly looking for a replacement for Lukaku.
Lukaku injury is certainly a major blow for Napoli, as he is a key player in the attack. Being out for three months is certainly not a short time as Napoli will have to play many matches without Lukaku. According to reports Napoli will not even include Lukaku in their UCL squad for the group stage. Hopefully Conte can handle this well especially ahead of their opening Serie A away match against Sassuolo.