updated 3:08 p.m. ET July 22, 2006

SEATTLE - The Boston Red Sox placed starter Tim Wakefield on the 15-day disabled list Saturday because of a stress fracture in the area of his rib cage.

The move is retroactive to Tuesday, meaning Wakefield is eligible to return to the rotation on Aug. 1.

The team purchased the contract of left-hander Kason Gabbard from Triple-A Pawtucket to start him Saturday against the Seattle Mariners in his major league debut. The 29th-round choice in the 2000 draft is the third Triple-A call-up to join Boston’s battered rotation in the last six weeks.

Kyle Snyder (2-1) beat the Mariners on Friday night, and Jon Lester (5-0) will start the series finale on Sunday.

Manager Terry Francona said Wakefield will begin undergoing ultrasound and hydrotherapy with Red Sox rehabilitation coordinator Scott Waugh on Monday. Francona said a bone scan revealed the right-handed knuckleballer has had “significant healing” in the rib cage area, which has bothered him for weeks.

“The No. 1 thing is get him to have range of motion without pain,” Francona said.

Wakefield, who will turn 40 on Aug. 2, left his last start Monday against Kansas City after four innings. He is 7-8 with a 4.14 ERA in 19 starts this season.

This is just the second stint on the disabled list in his major league career. Right elbow inflammation sidelined him from April 23-May 6, 1997.

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