After a 4-0 thumping of Norway last week, France's tournament preparations looked to be running smoothly, but they were rocked at the weekend by news that Ribery is struggling with a back problem.
The injury caused him to miss the 1-1 friendly draw with Paraguay on Sunday, although head coach Didier Deschamps remains optimistic the Bayern Munich man will be fit for their opening Group E fixture against Honduras on June 15.
Matuidi knows full well how important Ribery is to the team's cause.
"I'm not a doctor but I know that mentally Franck Ribery is fine," he said.
"You noticed that he did not train but the staff are doing everything in their power to make him ready for the last friendly (against Jamaica on June 8) or for the first game of the World Cup.
"We hope he will be fit, because Franck is a great player - we know we need him, we are all aware of it.
"Mentally he's with us and I hope he'll be there."
