After missing all of last season because of knee surgery, Portland Trail Blazers center Greg Oden injured his foot in his first regular-season NBA game and will be sidelined two to four weeks.

The team said Wednesday that MRI and computerized axial tomography scans confirmed Oden has a mid-lateral foot sprain.

Oden was injured in the first quarter of the Blazers’ 96-76 season-opening loss to the Los Angeles Lakers on Tuesday night.

‘‘I was trying to go get a rebound, and kind of came down on Derek Fisher’s foot on like the third play of the game. I kind of fell and didn’t think twice about it,’’ he said after the game.

Oden missed four field goals and two free throws in 13 minutes of play. So he is still searching for his first NBA point.

The 7-foot center was the top pick in the 2007 draft, but before his rookie season started, it was postponed by microfracture surgery on his right knee.

Trail Blazers coach Nate McMillan had not yet heard of the MRI results when he addressed reporters Wednesday at the team’s practice facility in Tualatin, Ore.

‘‘You don’t want injuries, and he’s worked so hard throughout this summer to get himself back,’’ McMillan said. ‘‘And we tried to do everything we could to get him ready for the season and the opener, and he steps on a guy’s foot.’’

Blazers guard Brandon Roy, who also spoke before the tests were complete, said the team will prepare to move forward without Oden for Friday night’s home opener against San Antonio.

‘‘I feel bad for him,’’ Roy said. ‘‘I know this is a big year for him and he had a lot on his shoulders.’’

The Trail Blazers also said in a release that Oden’s MRI revealed a couple of avulsions, or fractures, that ‘‘are not believed serious and do not require surgery.’’

Oden could not immediately be reached for comment.

His first game was highly anticipated by Blazers fans, who had to wait to see the top draft pick. The team had not had a No. 1 pick since 1978, when it chose center Mychal Thompson of Minnesota.