The Bosnia-Herzegovina international was forced from the field 16 minutes into Saturday's 2-1 defeat at the hands of Hannover in Schalke's opening Bundesliga match of the season.
Subsequent tests revealed a tear and Kolasinac is expected to undergo surgery on Tuesday.
The 21-year-old, who featured twice for his country at the World Cup in Brazil, made 24 league appearances for Schalke last season.
Kolasinac was quoted during the close-season as saying he had been offered a move to the Premier League with Manchester United.
However, that transfer failed to materialise, with the player eventually remaining at the club where he has spent his entire professional career.
'Obviously Messi is the best player in history and being compared to him means that you're doing things right, but I try to be myself': Barcelona star responds to comparisons with Argentine legend
'Darwin Nunez would be gold for Arsenal': Liverpool legend claims Gunners should have signed Uruguayan striker in January
