McCartin suffered the injury in the first quarter against Port Adelaide yet played out the rest of the game.
St. Kilda’s General Manager of Football Simon Lethlean said the club will reassess McCartin at the end of the week.
Lethlean said the “frustrating setback” should only sideline the forward for two or three weeks.
McCartin has had troubles with injury since being drafted in 2014 first overall, reducing him to 35 games since debuting in 2015.
St .Kilda faces bottom placed Carlton on Friday night at Etihad Stadium.