The Chelsea right-back is to be assessed after being forced off hurt in the Crystal Palace draw last weekend in what looks like a muscle problem.
The French Football Federation announced that the Blues right-back was among three withdrawals from the Under-21 squad as they face Slovenia and Bosnia and Herzegovina in two crucial European Championship qualifying games.
Gusto wasn't the only player who withdrew however after Burnley centre-back Maxime Esteve and Lens midfielder Andy Diouf also dropped out which leaves new coach Gerald Baticle with a number of decisions to make.
Sevilla midfielder Lucien Agoume is set to join the young Les Bleus on Tuesday instead as France weigh up their options ahead of two vital games.
Blues boss Enzo Maresca spoke about Gusto's injury and what might be the cause of it.
"With Malo, we will see now what happens. It looks like a muscle problem, so we will see."
France have confirmed Gusto's issue as a thigh problem which means he will miss both games as he takes time to recover.
Chelsea don't play their next match in the top flight until September 14th when they face a tough Bournemouth side in which new loan signing Jadon Sancho could make his debut for the club after leaving Manchester United.
