Ohio State big man Jared Sullinger has been medically flagged by NBA doctors who have expressed concern over the player's back, multiple league sources told ESPN.com on Monday.

Sullinger, who is projected to be a lottery pick in the draft on June 28, underwent a series of medical tests at the draft combine a week ago. A number of NBA team doctors have reviewed the information from the NBA and have told their front office staff that Sullinger's back issues could shorten his NBA career, and some have advised their teams not to draft him in the first round.

Sullinger's agent, David Falk, told ESPN.com by phone that he was not in a position to comment on the story.

Sullinger's father, Satch Sullinger, said he believes the issue isn't that serious.

"He had a bulging area that was due to his hamstring and quads being so tight," Satch Sullinger told ESPN.com senior college basketball writer Andy Katz in a phone call Monday afternoon. "It pulled on his hip flexor and he's been taking care of it to loosen it. You can call it a red flag if you want. But it's tight hamstring and tight quads. He's been to doctors, he's doing yoga and deep tissue massage. The flexibility is helping take the pressure off the area.

"We've got nothing to hide. At this stage it's all about what they can't do. Jared is a skilled player. A two-time All-American. He can play."