Colchester midfielder John-Joe O'Toole faces up to nine months on the sidelines after suffering ruptured cruciate ligaments.
The 21-year-old was stretchered off during the first half of Colchester's 1-0 defeat at Charlton on Tuesday night and a scan has confirmed the extent of the injury.
"It's a blow for him and a blow for us," said Us manager Aidy Boothroyd. "But it's part and parcel of football and we have to make sure that when he comes back, we're playing in a different league next season."
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