The on-loan Wigan frontman limped out of Town's last league game, the 1-0 win at Tranmere two Saturdays ago.
Lang, 21, underwent surgery yesterday after advice from a specialist and will not return to action until 2020.
The centre-forward has made a positive impression since his deadline day loan to Montgomery Waters Meadow and boss Sam Ricketts admits he will be a big miss.
“Langy has started really well for us and has been a great addition to the squad," said Ricketts, whose side return to action after the international break at Lincoln City on Friday.
“It is a real disappointment for Langy, and for us, that he will be out of action for a while.
“We will give him all the support and help to make sure that he comes back stronger from this setback.
“We have really good options in the forward line and this will give someone else a chance to step up.”
Lang is one of seven forward options in Ricketts’ ranks, including Lenell John-Lewis – who is on his way back from an ACL injury – and winger Shaun Whalley, who played in a front two at the beginning of the campaign.
Fejiri Okenabirhie has recently made a scoring return from a hamstring injury, while Steve Morison has not made any of the last four matchday squads.