FOXBOROUGH, Mass. — Tom Brady walked off the field under his own power. Several teammates didn't think he was hurt badly when he grabbed his left knee after being knocked down.
Yet the possibility that the New England Patriots might lose their star quarterback caused a scare at the team's joint practice with the Tampa Bay Buccaneers on Wednesday.
A person with knowledge of the injury said an MRI was negative and Brady was day-to-day with a left knee sprain. Asked if Brady might play Friday night in an exhibition game against the Buccaneers, the person said he didn't know.
The person spoke on condition of anonymity because the Patriots didn't make an announcement.
The two-time league MVP had a season-ending injury to the same knee in the 2008 opener.
Brady was injured midway through practice Wednesday when left tackle Nate Solder was pushed into him by Tampa Bay defensive end Adrian Clayborn. Brady, entering his 14th NFL season, fell, rocked backward on the ground and held his left knee.
He went to the sideline then returned for a few more plays before talking with coach Bill Belichick and leaving the field toward the team's indoor practice facility next to it.
"You've always got to stay away from the quarterback (in practice)," Clayborn said. "You got a guy on his heels and my instinct is to keep going, so that's what I did."
The contact came just as Brady threw a long incompletion down the right sideline toward rookie Aaron Dobson.
"We're always working to protect," Solder said. "I'll have to see what happened on the film. I screwed some things up here and there."
In 2008, Brady tore the anterior cruciate ligament in his left knee. The Patriots missed the playoffs that season. He has played every game since then and the team reached the playoffs in all four seasons.
New England is favored to win the weak AFC East for the 10th time in 11 years. Losing Brady would have made that much tougher.
After Brady left the field, third-year pro Ryan Mallett played with the first offensive unit and Tim Tebow, on his 26th birthday, played with the second team. Mallett threw an interception soon after taking over.
"Anytime anybody, especially a teammate, goes down it's a dark cloud. It's unfortunate," Patriots running back Shane Vereen said. "He went back out there, but we'll see."
San Francisco 49ers defensive lineman Demarcus Dobbs said he agrees with the NFL's decision to suspend him for one game without pay for a violation of the NFL's substance abuse policy that happened last season.
He must sit out the team's Week 1 game against Green Bay.
Dobbs was arrested Nov. 30 — his 25th birthday — for suspicion of driving under the influence and possession of marijuana.
The 49ers, in announcing the penalty jointly with the NFL, said Dobbs would be eligible to return to the active roster on Sept. 9, a day after the reigning NFC champion Niners' season opener at home against the Packers. He can still practice with the team, attend meetings and other activities.