Phoenix ? Four-time NL Cy Young Award winner Randy Johnson will have arthroscopic knee surgery today and miss three-to-six weeks.

The Arizona left-hander, who was 24-5 last season, won his first game in three decisions Sunday after spending two weeks on the disabled list.

The operation in Phoenix will be performed to clear out debris that caused an inflammation in his right knee.

“We’re hoping the procedure will eliminate the cause of the swelling,” Diamondbacks manager Bob Brenly said Wednesday night. “He’s taking this about as well as you’d expect. I mean, this is one of the great competitors in our game.”

Johnson was not at the ballpark, where the Diamondbacks are playing the Florida Marlins, and the team said he would not be available for comment.

The Diamondbacks said head team physician Michael Lee would perform the cleanup, but refused to divulge the time or location.

“Really?” Arizona first baseman Mark Grace said about the news. “That’s really bad.”

Rookie Brandon Webb, who pitched seven scoreless innings and beat the New York Mets 6-1 on Sunday in his first major league start, will replace Johnson in the rotation and start Friday’s game, the opener of a home series against Atlanta.

Webb struck out 10 — a Johnsonesque performance — before Johnson pitched the second game of a doubleheader at Shea Stadium.

Johnson struck out 12 — his 188th double-digit game — and beat the Mets 7-3.