Gronkowski will undergo an MRI scan on the injury later today having been carted off the field in the third quarter of his side's dramatic 27-26 win over the Cleveland Browns yesterday.
FoxSports has reported that the two-time Pro Bowler had torn his ACL, which would rule him out for the remainder of the season, but coach Bill Belichick has refused to confirm the severity of the injury.
"Rob was taken to the hospital for observation and evaluation on his injury. That's all I have on it," he told reporters.
The Patriots scored two touchdowns in little more than a minute at the end of the fourth quarter to rescue a dramatic victory, keeping their unbeaten home record alive in the process.