Nadal has been dealing with a hip injury he suffered at the Australian Open in January, and fears that the Spaniard may miss the Paris Grand Slam grew after he pulled out of this week's Italian Open.
Nadal skipped last week's Madrid Open and also missed tournaments at Indian Wells, Miami, Monte Carlo and Barcelona.
"It would be brutal, it would be tough for tennis if Rafa isn't going to be there," 20-time Grand Slam winner Federer told Sky Sports on Sunday at Formula One's Miami Grand Prix.
"I still hope so, I saw he pulled out of Rome so I wish him the best.
"Obviously Novak (Djokovic) hasn't been playing that much so I hope he's going to be strong as well and then all the young guys coming through as well," added Federer, who retired from tennis last year.
Nadal has competed at the French Open every year since winning the first of his men's record 22 major titles in Paris in 2005. The claycourt major begins on May 28th.
