I just read this on F1Live.com...it looks like Rossi will have to wait a bit longer:
Max Chilton will race this weekend after Marussia reversed its decision to give his drive to Alexander Rossi at the Belgian Grand Prix.
Rossi took part in FP1 but will hand the car back to Chilton for the rest of the weekend, meaning the American will not make his debut after all. On Friday morning the team formally applied to change its driver nomination back to Chilton for the rest of the weekend.
Spa would have been a great track for Alexander to make his first start. Perhaps he will get his chance at the USGP?