FOXBOROUGH — Patriots quarterback Tom Brady left practice early Wednesday, several minutes after suffering a left knee injury at the end of a passing play.
Two league sources said Brady suffered a sprain and the injury is not considered serious.
Team president Jonathan Kraft told reporters about an hour after practice, “I’m under the impression that it’s probably not that serious, but that’s not a definitive answer.”
The injury happened during 11-on-11 work, with the Patriots practicing in full pads against the visiting Tampa Bay Buccaneers. Brady was looking to his right, and threw a long pass toward Aaron Dobson, when to his left, tackle Nate Solder was bull-rushed by Tampa Bay defensive end Adrian Clayborn.
Clayborn pushed Solder backward, right into Brady, who went down to the grass. Brady rocked backward and then sat there for a minute holding his left knee.
Brady was not wearing the bulky black brace he has worn in games since coming back from the torn ACL he suffered in that same left knee in the 2008 season opener; he was wearing a gray sleeve over the joint.
Brady sat out one snap, then returned, but he touched the knee in between plays. He completed three passes and made a handoff before consulting with coach Bill Belichick, offensive coordinator Josh McDaniels, and head trainer Jim Whelan. After a brief talk, Brady walked gingerly off the field with Whelan in the direction of the Dana-Farber Fieldhouse.
It is not known if Brady went into the fieldhouse or was transported back into the team facility via golf cart or other means; the access road that runs behind the practice fields is not visible to those watching practice.
Backup quarterback Ryan Mallett handled the first-team snaps for the remainder of the session.
Solder said it is worrisome anytime a teammate goes down with injury. The third-year player had some obvious struggles during the play on which Brady was injured, which he admitted.
“We’re always looking to protect,” Solder said. “I’ll have to see what happened on film. I screwed some things up here and there. We’ll work through that.”
Clayborn, who did nothing wrong or malicious on the play, explained what happened.
“You know you’ve got to stay away from the quarterback,” he said. “But if you’ve got a guy on his heels, my instinct is to keep going. That’s what I did.
“[It was] a bull rush. The tackle backing up, apparently he tripped on Brady and he fell on me.”
Former Buccaneer LeGarrette Blount, now with the Patriots, did not believe his old teammate, Clayborn, deliberately tried to hurt Brady.
“They talk to us about it every day [staying clear of the quarterback as much as possible],” Blount said. “I guess there’s always somebody that makes a mistake and goes into the quarterback. None of it is on purpose. It’s an accident.
“It’s guys practicing hard. They emphasize it a lot but accidents happen. I’m sure it wasn’t on purpose.”
The incident immediately prompted several Las Vegas casinos to temporarily take Patriots wagers off the boards.
Before the week began, Belichick and Bucs coach Greg Schiano talked about keeping physicality in check from both sides, just as Belichick did with Eagles coach Chip Kelly last week. Notably, any players involved in a fight were to be benched for the rest of that practice.
There was to be minimal contact with quarterbacks, Schiano said.
“Coach Belichick and I stressed to our teams to let [the quarterbacks] throw the ball — rush the passer but don’t get around him,” Schiano said. “I can’t tell you because I didn’t see what happened. I’ll look at it on tape. I hope he’s OK.”
It isn’t known whether Brady will play in Friday’s preseason game with the Buccaneers, though it is likely the Patriots will take every precaution with their star.
A fan-recorded video of the play ends with a male and then a female saying, “Oh no,” as they watch Brady tumble to the ground, and that sentiment was shared by fans far and wide — as Brady goes, so go the Patriots. But it appears the worst-case scenario has been avoided.
The Globe's Ben Volin contributed to this report.