Setup man David Robertson is out for the banged-up Yankees' series against the Oakland Athletics because of a sore left hamstring, leaving Mariano Rivera as New York's only regular late-inning reliever available against the defending AL West champions.
Seventh-inning specialist Joba Chamberlain was officially placed on the 15-day disabled list Friday, retroactive to April 28, by New York because of a right oblique strain.
The Yankees have 10 players on the DL.
Robertson hoped he would only miss a couple of days, but manager Joe Girardi says Robertson would be unavailable at least until the Yankees begin a series at Colorado on Tuesday.
The Yankees purchased the contract of right-hander Preston Claiborne from Triple-A Scranton/Wilkes-Barre. To make room on the 40-man roster, New York designated righty Cody Eppley for assignment.