Crossley managed to play in Forest's 1-1 draw against Middlesbrough at the Riverside Stadium on Monday night, but he is suffering from a slipped disc which is preventing him from training in between matches and has told Bobby Gould, the Wales manager, that he will not be joining up with the squad.
Crossley intends to nurse himself through relegation-threatened Forest's remaining five league games before having treatment for the injury.
"I'm gutted about it but I've had to drop out of the Wales squad," said Crossley, who made an impressive international debut in last month's friendly against the Republic of Ireland. "I've spoken to Bobby and he knows what the situation is."
Gould, anticipating Crossley's problems, included four goalkeepers in his original squad in Neville Southall, Crossley, Andy Marriott and Paul Jones, and he is also hoping that Mark Hughes will recover from a groin strain in time to face the Belgians.
Hughes appeared as a second-half substitute in Chelsea's 1-0 defeat at Middlesbrough at the weekend despite his injury, but will delay joining the squad.
"Mark is staying at Chelsea for treatment for the next couple of days, but I'm still hopeful that he'll be fit for Saturday," Gould added. He has called up the Huddersfield midfielder Marcus Browning in case Hughes has to drop out.
Belgium could be without the Newcastle centre-back Philippe Albert, who suffered a knee injury during Sunday's 1-1 with Wimbledon.
Arsenal's Patrick Vieira and Franck Leboeuf of Chelsea were both named in France's provisional squad of 37 for next year's World Cup, but there was still no place for Eric Cantona or David Ginola.
From the list, Aime Jacquet will pick a reduced squad of 18 for the friendly international against Sweden at Parc des Princes next Wednesday.Reuse content