"Kind of a super-utility that gives us some flexibility all around the diamond," manager John Farrell said prior to Sunday's rubber match against the Tigers at Fenway Park.
In 53 Minor League games this season, Weeks was batting .210 with one home run and a .619 OPS.
With Dustin Pedroia landing on the disabled list Saturday with an aggravated right hamstring, the Red Sox played Saturday's game while employing a three-man bench and an eight-man bullpen.
Weeks, who is 28 years old, becomes Boston's lone backup infielder and fills the final slot on the 40-man roster, vacated when catcher Sandy Leon was designated for assignment on Monday.
Ramirez made three appearances in his first big league callup and allowed three runs in five innings.
Aaron Leibowitz is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.