Miami ? Pat Riley is taking a break from a season that has left him limping and in pain.

The Miami Heat coach began an indefinite leave of absence Wednesday because of hip and knee problems, choosing assistant Ron Rothstein to fill his spot on an interim basis.

Riley will have surgery Friday to remove floating chips his right knee. Surgery on his hip, the malady that hurts him most now, is not yet scheduled. The 61-year-old coach doesn’t know how long he’ll be out.

“I’m going to be displaced for a while, but not disconnected at all,” he said.

Miami’s record fell to 13-18 on Wednesday after a 110-95 loss to the Los Angeles Clippers. Already this season, the Heat have seen Shaquille O’Neal, Dwyane Wade and Jason Williams – perhaps the three biggest keys in last year’s championship run – miss many games with injuries.

And now it’s Riley’s turn.

“We have a championship team that is sideways right now, so this is going to be a great challenge,” Riley said. “Keep your notebooks open. We’ll see how it plays out.”

Riley, who also is the Heat president, is in his 12th season with the organization and 10th year as its coach. He resigned as coach shortly before the 2003-04 season, then returned to the bench in December 2005, replacing Stan Van Gundy and postponing right hip replacement surgery.

In September, Riley said he didn’t expect to need the operation this season, but the pain apparently has worsened in recent weeks. He considered surgery during the summer, then simply decided against it.

“I’m just tired of the pain and the medication,” Riley said.

Rothstein was the Heat’s first head coach in the 1988-89 season and lasted three years with the expansion franchise, finishing with a 57-189 record. His last full stint as an NBA head coach was with the 1992-93 Detroit Pistons, a team he guided to a 40-42 record, and he filled in for Riley for the final two games of last season while the coach visited his ailing mother.

Riley’s frustration has grown as the Heat have struggled this season, remaining mired below .500. But he said Wednesday the team’s record did not factor into his decision to temporarily step aside now.

“We’ve had defensive lapses that are mind-boggling to me,” Riley said. “The offensive output will be corrected when Shaq and Dwyane and everybody’s healthy. I don’t think there’s been any question about that. But I haven’t been happy with our overall effort and defense all year long, from the get-go.”

The Heat haven’t had their preseason projected starting five together for any games yet this season because of all the injuries.

Wade, last season’s finals MVP, missed his third straight game Wednesday because of a sprained wrist. A six-game Western swing will begin Friday in Phoenix, and the team hopes to get O’Neal back by the end of the trip.

“I haven’t been happy about the situation,” Riley said. “I don’t think anybody is. I hope that when everybody gets healthy, including myself, it’ll rectify itself.”

Riley has a career record of 1,164-606. Last season’s title run was vindication for Riley, who made sweeping roster changes after the 2005 playoffs. The championship was Riley’s seventh and his fifth as a head coach.