Foulke, who signed a one-year deal with the A's just before the opening of Spring Training, recorded a save against the Toronto Blue Jays on the 10th, but hasn't been able to get back on the mound since. He has an ERA of 2.57 and had six strikeouts in seven innings.
The A's will make a corresponding move before Tuesday's home game against the Minnesota Twins.
Foulke is eligible to come off the DL on Saturday, the same day right-hander Justin Duchscherer, currently on the DL with a strained right biceps, is slated to make his next start after coming off the disabled list.
Duchscherer travels to Las Vegas to make a rehab start with Triple-A Sacramento on Monday night. His pitch count is between 50 and 60.
"I've had no problems since I started throwing," Duchscherer said. "I took six days off since the strain and have been throwing since. My last bullpen session [Saturday] went well.
Geren said the only sure thing is Duchscherer's rehab start. He wouldn't discuss Duchscherer's possible start on Saturday in Seattle against the Mariners.
Duchscherer said, however, he'll have a 75-80 pitch count when he faces the Mariners.
Foulke has been troubled with injuries since his 32-save season with the Boston Red Sox in the 2004 world championship year.
He needed surgery on both knees during the 2005 season, missing over 50 games. He had elbow tendinitis and a stiff back for much of the 2006 season, and retired from baseball in February 2007 instead of sitting on the disabled list with the Cleveland Indians all year.
Rick Eymer is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.