The Patriots aren’t waiting around to replace injured star tight end Rob Gronkowski, whose injury appears to be season-ending.

A league source confirmed that Gronkowski tore his ACL and also suffered damage to his MCL, which Pro Football Talk and ESPN earlier reported, and will have a lengthy rehabilitation process this offseason that could put his availability for the start of the 2014 season in question.

“Rob’s going to have more tests today, but that situation doesn’t look too good,” Patriots coach Bill Belichick said Monday.

The team is bringing back journeyman tight end D.J. Williams, a league source told the Globe.

Gronkowski took a hit from Cleveland’s T.J. Ward squarely in his knee in the third quarter Sunday, and was carted off the field. He had 39 catches for 592 yards and four touchdowns in seven games this year after sitting out the first six games with back and forearm injuries, and will likely finish his season on injured reserve for the second straight season.