Lions physio Bobby Bacic confirmed the news on Sunday but added that right-back Shaun Cummings may yet play again this term.
Both players missed the goalless draw at Cardiff on Saturday and Bacic told the club’s official website: “Both injuries were picked up during the win over Wigan.
“Unfortunately Williams won’t feature again in 2014/15 after suffering a freak injury when colliding with the perimeter wall. He has sustained an impact fracture more common in snowboarders landing from height rather than footballers.
“We will give another update on his condition later next week after he has a review with the surgeon, but we expect to let the bone heal naturally.
“Cummings has a tear in a groin muscle and is working extremely hard so he can still play some part before the season ends.”