Fulham manager Roy Hodgson says he is worried Andy Johnson could be ruled out for the rest of the season if an exploratory operation reveals he needs knee surgery. The former Everton striker had just been getting back to full fitness following a previous injury but will now undergo a procedure to discover the full extent of his current problem. Hodgson is hopeful that it will just be a cartilage problem which could see Johnson back by the end of February. However, if it is bad news, as Hodgson fears, the 28-year-old will require knee surgery and will be out for the rest of the season. "AJ's going to have an exploratory operation on his knee," said Hodgson. "If they find that the problem is as major as it could possibly be, then he would need an operation that would keep him out for the rest of the season. "If we're lucky and the major operation is not needed, and it's something wrong with the cartilage, then he might be back earlier. "At the moment we're talking three to four weeks, and the worst-case scenario is the rest of the season and him being fit to join us in pre-season." Hodgson already has six first team players sidelined through injury and is cursing his luck after allowing Diomansay Kamara to join Celtic on loan. "One of the reasons why we let Diomansy go was because we didn't think the problem with Andy was anywhere near as grave," he added. "I was concerned that I would not be able to give Diomansy regular games, so when a club of Celtic's stature comes in for him, it is very difficult for me to say 'you have to stay'. "Of course now I have let him go and have further news about Andy, I might be beginning to regret it, but you can only make decisions at the time."