Assistant Ron Rothstein will assume head coaching duties on an interim basis while Riley receives treatment on his painful right knee and left hip, the team said on its Web site (www.miamiheat.com) on Wednesday.

Riley, who guided the Heat to the NBA championship in June, is scheduled to undergo knee surgery on Friday.

The 61-year-old coach is also likely to have a hip replacement soon after, according to the Sun-Sentinel newspaper.

Riley's absence is another setback for the struggling Heat (13-17), who have played most of the season without injured All-Star Shaquille O'Neal.

It marks the second time Riley has left the team in mid-season.

He stepped down as coach in October 2003, handing over the reins to assistant Stan Van Gundy.

Riley, who also led the Los Angeles Lakers to four titles, returned to the bench when Van Gundy resigned for personal reasons in December 2005.

In 23 seasons as a coach with the Heat, Lakers and New York Knicks, Riley has compiled a regular-season record of 1,164-606 while going 171-107 in the post-season.