The Patriots announced Gronkowski will undergo X-rays and will not return to the game. An ESPN video showed Gronkowski walking from the X-ray room to the Patriots' locker room with a slight limp.
Gronkowski suffered the injury with 2:49 remaining in the contest, when Denver defensive back Darian Stewart hit him low on an incomplete pass. Gronkowski's leg whipped back as it made contact with Stewart.
Gronkowski immediately writhed in pain on the ground before being tended to by the Patriots medical staff and eventually carted to the locker room. Patriots quarterback Tom Brady and coach Bill Belichick came to check on Gronkowski in a reflection of the severity of the situation.
Losing Gronkowski would be a devastating blow for the Patriots, though they have experience playing without him. Gronkowski broke his forearm Nov. 18, 2012, and tore his ACL on Dec. 8, 2013.
The Patriots, who entered the game with a 10-0 record, already have been decimated by injuries to star receiver Julian Edelman, starting left tackle Nate Solder, running back Dion Lewis and receiver Danny Amendola.