Bristol City full-back
Mulgrew has succumbed to the Achilles injury that kept him out of Celtic's draw against Hibernian last weekend and will miss the opening World Cup qualifier against Serbia.
Former Aberdeen captain and Rangers player Foster, 27, is uncapped.
The versatile Mulgrew joins a number of full-backs unavailable to manager
Levein called up Huddersfield left-back
FIFA World Cup
A US man trying to dribble a football 16,000 kilometres to Brazil in time for the 2014 FIFA World Cup has died after being hit by a pickup truck on the Oregon Coast.