Roberts sprained his right wrist, while Bowe suffered a strain of his left elbow. Both players have been receiving intensive treatment and are hopeful of recovering in time for the third Test in Johannesburg this weekend.
If Roberts is ruled out then the Lions will be looking for a completely new centre pairing having already lost Brian O'Drsicoll through concussion. Lions head coach has three alternatives to turn to in that case, two from Magners League clubs.
Munster's Keith Earls has played both outside centre and full back on tour, while Leinster's Gordon D'Arcy is a candidate for the inside centre berth against London Wasps and England star Riki Flutey.
If Bowe fails a fitness test then the Ospreys' Shane Williams could come in for his first Test start on the tour.
