The 26-year-old also has a groin problem, picked up during the 3-1 loss at Southampton last weekend.
He was then left with two broken fingers and an arm in a sling after reportedly lashing out in the away dressing room at half-time.
Newcastle are one place off the bottom of the table with six games to play.
A Newcastle statement confirmed the Netherlands international was receiving treatment for both injuries.
"Janmaat will be unavailable for the club's forthcoming fixture against Swansea at the weekend," the statement said. "He will be reviewed further next week and the club will provide an update in due course."
Newcastle defender Daryl Janmaat will miss Saturday's visit of Swansea with two injuries, including broken fingers after reportedly punching a wall.