The right back, who has arrived in South London from Swindon Town this summer, will find out the extent of the knock next week but will have to recover to return to the first team squad after the third tier season has begun.
Ben Garner explained the situation around Egbo’s injury when he spoke to the club’s media team following the Addicks’ 4-2 win at Colchester United on Tuesday evening.
He said: “There’s a fairly significant injury to his knee which is the big disappointment of pre-season so far.
“He’ll have a period of time out, he’ll see a specialist next week, we don’t think it’ll need an operation, we’re almost certain it won’t, and it’ll just be a case of rehabbing as quickly as possible.
“He’s got a great attitude, he really has, he’s so positive and he will do everything possible to get back quickly, and we’ll support him on and off the pitch and get him back as quickly as we can.
“It’ll be weeks (not months), I never like to put a timeframe on it.
“He’ll certainly miss the start of the season and then it’ll be a case of getting him back as quickly as we can.”
The Addicks are well-prepared to deal with Egbo’s absence, with Sean Clare, Steven Sessegnon and Lucas Ness, who has been playing with the first team in pre-season, available to slot in at right back.
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If Charlton can start the season quickly, despite a difficult opening seven fixtures, it could be tough for Egbo to earn a starting berth for a while.
Left back is the main position of concern for the Addicks with the opening game of the season just over two weeks away, and Egbo, a right back, and Charles Clayden, a young winger who spent time on loan at Wealdstone last term, seemed like the most likely players to fill the void should a signing in that position not be acquired before the start of the campaign.
The injury could potentially provide an opportunity for Clayden, 21, to knuckle down and earn his first league starts for the club at the end of this month.