Following on from Caterham announcing Andre Lotterer for Spa, Marussia have now also swapped a driver with Alexander Rossi coming in.
Rossi joined Marussia last month as their reserve driver and was done to take part in a Friday pracitce or two.
But in light of 'contractual issues' with Max Chilton, will now contest the Belgian Grand Prix wekeend.
"It goes without saying that I am thrilled to be given the opportunity to race in Formula 1 for the first time and I cannot thank the Marussia F1 Team enough for the faith they are demonstrating in me," said the American.
"It's a very big moment for me and there's a lot to prepare in a short space of time, but on the other hand I have felt ready for this for quite a while now
"It is also exciting to be given this opportunity at such a fantastic and historical circuit as Spa-Francorchamps. I can't wait to drive the MR03 from tomorrow and I hope to reward the team with a solid race weekend."
Meanwhile team principal John Booth confirmed that Rossi's run in the car would end as soon as Chilton's situation is resolved.
He said: Although it was not our intention to offer Alexander the possibility to race this season, in light of the circumstances we are pleased to be providing him with the opportunity to make his grand prix debut at this weekend's Belgian Grand Prix in Spa-Franchorchamps.
"Naturally we hope to resume normal service with respect to our established race driver line-up as soon as possible, but for now we wish Alexander well for the weekend ahead and we look forward to seeing him in action."