"Just got a bit of a little tweak," Caldwell said Saturday morning. "He won't play in the game obviously, but he'll be back soon."
Clark immediately received medical attention at practice Friday and left on a cart with a wrap around his upper left leg.
Clark tied wide receiver Reggie Wayne for the team lead in receptions (100) and touchdown catches (10) last season. Clark's 1,106 receiving yards were second-most on the team.
In addition to Clark, seven other Colts were declared out by Caldwell, who added there is only a slim chance of safety Bob Sanders playing. Defensive end Dwight Freeney and wide receiver Anthony Gonzalez didn't practice Saturday and also might not play.
The list of players who will not play includes defensive tackle Keyunta Dawson, wide receiver Pierre Garcon, linebackers Clint Session and Ramon Humber, offensive tackle Charlie Johnson, center Jeff Saturday and offensive lineman Jacques McClendon.