It's after an alleged incident during last Sunday's LV= Cup final against Leicester.
England elite squad member Clark is accused of an act contrary to good sportsmanship for hyperextending Tigers hooker Rob Hawkins' arm during the game. Hawkins suffered a broken elbow.
In a statement, Saints confirmed they have started an internal investigation: "Following the completion of this investigation the club's management has suspended Calum Clark from playing until further notice. Northampton Saints will make no further comment about this issue."
Hawkins is not expected to play again this season as a result of the injury. Television footage of the game shows former Bath forward Hawkin in agony from a 21st-minute ruck.
Clark, in the immediate term, will miss Northampton's Aviva Premiership clash at home to Wasps on Saturday.
Northampton Saints are currently fourth in the table and pressing for a title play-off place.