Neal Ardley confirmed that Darius Charles was due to have an operation today after suffering a knee injury in training last week.
The experienced defender is likely to miss the start of the season with an injury that could keep him out until September.
Neal Ardley said: "Darius is due to have an operation today. In the off season we knew that he needed to come back fit and everything was fine, but he must have taken a wrong step in the first warm-up and his knee flared up. We decided to go all in and have an exploratory operation. They think that they know what the problem, but they may not know the extent until they carry out the operation. Fingers-crossed, it is exactly what they thought and he is back playing at the start of September."
Neal added that midfielder Tom Soares has returned to full training after missing the end of last season due to a hairline fracture of his distal tibia and Jon Meades (knee) is also making good progress.
"Tom is training fully with the squad," said Neal. "He is basically a week behind and will be playing a bit of catch-up. Jon is a little bit behind him, but he had an operation in the summer. They both know the importance of getting into the games programme quickly, otherwise they will be falling further behind. You can never guarantee that things will run smoothly, but if we can get them back to full fitness by the start of the season we will have a really strong squad to choose from."