Youkilis was once again a late scratch Monday night, only hours after initially being listed in the starting lineup.
Nick Punto will take Youkilis's place and start at third as Boston prepares to face young Oakland starter Tommy Milone. The A's lefty is off to a hot start this year, sporting a 3-1 record to go with a 2.00 ERA.
No Red Sox starters have faced Milone, who started just five games as a rookie in Washington last summer.
Buchholz, meanwhile, has a 7.84 ERA in five career starts against the A's. Daric Barton has enjoyed facing Buchholz, as he's gone 5-for-10 with four RBIs against the Red Sox righty.
Red Sox (10-11)
Mike Aviles, SS
Dustin Pedroia, 2B
Adrian Gonzalez, 1B
Cody Ross, RF
David Ortiz, DH
Kelly Shoppach, C
Darnell McDonald, LF
Marlon Byrd, CF
Nick Punto, 3B
Clay Buchholz, P
Athletics (11-12)
Jemile Weeks, 2B
Coco Crisp, LF
Josh Reddick, RF
Yoenis Cespedes, CF
Seth Smith, DH
Kurt Suzuki, C
Daric Barton, 1B
Brandon Inge, 3B
Cliff Pennington, SS
Tommy Milone, P