ST. LOUIS (AP) _ Oklahoma's Eduardo Najera was knocked unconscious and received a concussion in a violent collision with Michigan State's Mateen Cleaves during the NCAA Midwest Regional semifinal Friday night.

Doctors said Najera sustained a grade I concussion, a bruised breast bone and a chipped tooth as well as a cut on the chin that took six stitches.

At first, it was feared the 6-foot-8 junior had broken his jaw.

``He was conscious when I got to him and responsive,'' Oklahoma trainer Alex Brown said. ``All X-rays were negative and he will be further evaluated in Oklahoma tomorrow.''

The collision occurred as Najera set a screen in the backcourt. Cleaves, unaware of the screen, smashed at full speed into Najera and both players crumbled to the court.

Najera lay bleeding and unconscious on the floor for several minutes after Cleaves' head caught him flush on the chin. Cleaves, who had joked the day before that the game would be a ``good old-fashioned smashmouth football game,'' also lay nearly motionless for several minutes as Michigan State officials attended to him.

Cleaves returned to the game moments later but Najera, still woozy, went back to the lockerroom for additional treatment before returning to play.

``It was like I ran into a brick wall,'' Cleaves said after the Spartans won 54-46. ``It was a blessing both guys were OK.''

The crowd of more than 43,000 fell silent while officials attended to Najera and bandaged his bleeding chin.

``When I saw him on the floor, he was out,'' Oklahoma coach Kelvin Sampson said. ``Seeing him face down, blood coming out of his face, makes you realize what these kids mean to you. I wanted to make sure Eduardo was OK. My heart went out to him.''

Sampson said the Oklahoma lockerroom was ``very emotional.''

`He's got a gash from one side of his chin to the other. They were trying to get his chin put back together,'' he said.

It was the second time this year Najera had been involved in a violent play. During a game at Missouri, Najera swiped at the ball as Tigers guard Keyon Dooling went up for a layup and caught him on the head, knocking him out of the game.

Cleaves said he was glad to see Najera get back in the game.

``I wasn't knocked out. I was all right,'' said Cleaves, who returned with 6:54 remaining. Najera returned with 4:25 left.