SANTA CLARA, Calif. (AP) — Two San Francisco 49ers defenders with concussions could be done for the season.

Safety Michael Lewis sustained his third concussion of the season during Sunday’s 45-10 loss to Atlanta and was to have further testing during the off week. Linebacker Jeff Ulbrich, who suffered a concussion on the opening kickoff against St. Louis on Oct. 4, is scheduled to be seen by a neurologist on Wednesday.

It will be the first time the 10th-year player has been examined by a neurologist and Ulbrich said Monday he’s not ruling out retirement after sustaining more concussions during his career than he can count.

“I don’t know (how many),” Ulbrich said. “I don’t even really know what a concussion is. They ask me if it’s like seeing stars, but every linebacker in the NFL has five or six of those a game.”

Lewis, who sustained two concussions during an 11-day span in the preseason, could be sidelined for a prolonged period though coach Mike Singletary didn’t want to speculate Monday.

Ulbrich said he’s dealing with his health “day to day” and isn’t thinking about his football career beyond Wednesday’s exam. After that he might be forced to make a big decision.

He acknowledged he’s at a point in his life when he needs to think about his long-term health, future and family.

“I have to take all those things into consideration,” Ulbrich said.

Lewis led with his helmet on the hit Sunday and was face down on the field for several minutes while being examined. He eventually sat up and was helped off the field, appearing dazed. Athletic trainers ran a series of tests on Lewis as he sat on the sideline.

Singletary said Monday a player is at risk for serious injury leading with the head down.

“A third concussion. Once again, it was a situation in which he did have the concussion, and afterward, he cleared right away, meaning that he was coherent,” Singletary said. “He understood everything that was happening, which is a very good sign. So, now it’s one of those things we have to really look at and watch day to day and see where it goes.”

Lewis’ first concussion occurred Aug. 18 during a joint practice with Oakland at the Raiders’ training site in Napa when he got hit by a fullback. He suffered another in an exhibition game at Dallas on Aug. 29, when he fell and took a knee to the helmet.

The 29-year-old Lewis, a Pro Bowl selection in 2004 with Philadelphia, is in his eighth NFL season and third with San Francisco. He ranked third on the team with 118 tackles in 2008.

Lewis recently expressed concern about his concussions and the susceptibility to having more considering his pattern.

“I’ve done some research on it as well. The studies are somewhat scary because you see athletes all the time dealing with some kind of problem resulting from a head injury,” he said. “You know it’s a possibility (to deal with these issues down the road). As a pro football player, there could have been numerous times you took hits to the head and it could have been a concussion and you didn’t know about it and you just played through it. Those things continue to add up over your career. You see guys like Dan Morgan who are forced to retire because of hits to the head. It’s a concern.”

Injured running back Frank Gore is expected to return to practice this week after missing the past two games with an ankle injury.

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