FOXBOROUGH, Mass. -- Patriots linebacker Dane Fletcher's season may have ended shortly after it began on Thursday night, when he left early in the first quarter apparently unable to put weight on his left knee.

According to multiple reports, Fletcher suffered a torn ACL, but teammates after the game were cautious to wait for an official diagnosis.

"It's so fresh right now, so I don't really want to talk about it," defensive end Rob Ninkovich said. "Obviously he hasn't an MRI yet or anything, so you really can't jump to conclusions on that."

Fletcher, a former undrafted free agent who is entering his third season with the team, had started at middle linebacker in Thursday's preseason opener against the Saints, in place of Brandon Spikes, who did not suit up.

"Great player, obviously. Special-teams guy that's always able to go out on defense that can contribute," Ninkovich said of Fletcher. "Just an overall good player that you would like to have for the whole season."

Linebacker Bobby Carpenter added: "Dane's been a great guy. He's really helped me a lot. (With) him and Jerod (Mayo), we have a really tight linebacker room. He's a tremendous guy and he's a really good player. Hopefully he'll be all right."

Safety Patrick Chung said, "Dane's good. He's a good, smart, physical, tough guy. Very intense."

Fletcher had 32 tackles in 10 games played last season, including five starts. Prior to his injury, Fletcher figured to be a key reserve option on defense as well as a consistent presence on special teams.

"He’s played on all four downs for us. He's played on first and second down, played on third down and played in the kicking game, so he has some versatility," head coach Bill Belichick said. "He's had roles on different downs on different times or different game plans."

If Fletcher's injury proves season-ending, it could further solidify Carpenter's chances for a roster spot, while also providing an opportunity for less-experienced players such as Jeff Tarpinian or Mike Rivera to make the squad.