Injury struck during the second half, when Cotterill was substituted for Jonathan Smith after hurting his ankle ligaments.
Full extent of the damage was being assessed today, making Cotterill an early doubt for Tuesday's league game with Reading.
The reserves drew 1-1 with Andreas Johansson on the score sheet. Ryan Taylor, Kristofer Haestad and Andreas Granqvist featured.
Check back later for a full in depth report on the reserves.
