49ers’ Bowman may not be ready to practice even if cleared

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Inside linebacker NaVorro Bowman had an MRI exam on his left knee Wednesday, but he wouldn’t necessarily make his practice debut Thursday if he received a positive medical report.

“Want to see where that’s at first,” head coach Jim Harbaugh said.

Bowman has spent the season on the physically-unable-to-perform list, rehabbing his knee after he tore the ACL and MCL in the NFC Championship Game in January. Once Bowman returns to practice, the 49ers have a three-week window during which they can activate him to the 53-man roster.

Bowman said Sunday he is still experiencing pain in his knee and doesn’t know when he’ll return to practice, ESPN reported. Harbaugh was asked if Bowman is still experiencing discomfort.

“I saw that reported,” he said, “But I don’t know for sure.”

Practice report: Cornerback Tramaine Brock is expected to miss Sunday’s game against the New York Giants with a hamstring injury, a source said.

49ers' NaVorro Bowman speaks with reporters during the daily press conference on Thursday Jan. 31, 2013, in New Orleans, La. The San Francisco 49ers and the Baltimore Ravens prepare for this Sunday's NFL Superbowl match up. less 49ers' NaVorro Bowman speaks with reporters during the daily press conference on Thursday Jan. 31, 2013, in New Orleans, La. The San Francisco 49ers and the Baltimore Ravens prepare for this Sunday's NFL ... more Photo: Michael Macor / The Chronicle Photo: Michael Macor / The Chronicle Image 1 of / 1 Caption Close 49ers’ Bowman may not be ready to practice even if cleared 1 / 1 Back to Gallery

Brock, who has missed six games this season with turf toe, was among two prominent cornerbacks who didn’t practice. Rookie Jimmie Ward was sidelined with a foot injury, and his status for Sunday is unknown. Ward had surgery on his right foot in March that kept him off the field until training camp. It’s not known which foot kept Ward sidelined Wednesday.

Rookie inside linebacker Chris Borland (shoulder) was limited and was in a non-contact jersey. Borland had a series of shoulder injuries early in his career at Wisconsin. In his first two seasons, Borland had three shoulder surgeries, two on his left shoulder.

At least one NFL team took the third-round pick off its draft board because it believed his left shoulder required another surgery, the Milwaukee Journal Sentinel reported in April.

Injury report: Nose tackle Ian Williams, who sustained a small fracture of his left fibula in Sunday’s win at New Orleans, was sporting crutches and a boot that extended to his left knee in the locker room.

Harbaugh said Williams could go on season-ending injured reserve, which he did last year after he sustained a broken left ankle and torn ligaments in Week 2, an injury that required four surgeries.

Rookie wide receiver Bruce Ellington was also on crutches and wearing a boot after he sustained a left ankle injury against the Saints. Harbaugh said he didn’t think Ellington would be placed on injured reserve.

Eric Branch is a San Francisco Chronicle staff writer.