The Bulgarian suffered an ankle injury during Monday's training session and was unable to join his team-mates as they went through their paces ahead of the friendly with the Seattle Sounders.
The injury that the striker has picked up is not a serious one, it has been described as “a knock” but coming so early after returning to training, no chances are being taken.
It is a blow for the player, he has been keen to show what he can do after not making the bench for last season’s Champions League final.