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04/09/08 4:20 PM ET

D-backs place Davis on disabled list

Lefty replaced by right-handed reliever Peguero on roster

PHOENIX -- The D-backs placed pitcher Doug Davis on the 15-day disabled list Wednesday and recalled reliever Jailen Peguero from Triple-A Tucson.

Davis will undergo surgery to have his cancerous thyroid removed Thursday. An exact timetable for his return is not known, but it's possible he could return to baseball activities in four to six weeks.

Peguero's stay could be a short one as the D-backs will need to make room on the pitching staff for Randy Johnson when he is activated from the disabled list prior to his start Monday. In the meantime, the right-hander will add some depth to the bullpen.

A long shot to make the team heading into Spring Training, Peguero impressed the staff, pitched well and was the team's final cut from the pitching staff.

A key to Peguero's improvement has been the development of a sinking fastball to go along with a low-to-mid 90s fastball and slider. Whereas he relied primarily on the slider last year, he seems to trust his fastball more now and has asserted himself as more of a power pitcher.

"He's got really good stuff," pitching coach Bryan Price said. "He had a great spring. I think the fastball makes his temperament more aggressive instead of passive as an offspeed pitcher. That's exciting because I think he's a guy in the long term that could really help our bullpen."

Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.