Cambridge United defender Rory McAuley could face surgery after injuring his knee at his nephew's birthday party.
McAuley, 22, has suspected cartilage damage after falling while playing with the three-year-old on Sunday.
"It is a freak accident. It is too swollen to be assessed properly at the moment," manager Jez George told BBC Radio Cambridgeshire.
"He will be seeing the specialist again on Monday and has no chance for Darlington on Saturday."
The versatile defender endured a similar setback ahead of the 2010-11 campaign, when he spent six weeks on the sidelines following surgery on the same knee.
McAuley can consider himself unlucky with injuries, after missing the start of the current campaign when he punctured his calf on a nail during training.
George can turn to Michael Wylde for defensive cover, although the former Tamworth man has been playing with a groin problem and requires surgery of his own.