The Spanish world three started the season brilliantly, with 20 straight victories before surprisingly losing the final in Indian Wells against 20-ranked Taylor Fritz on Sunday.
He suffered the injury in the semi-final against compatriot Carlos Alcaraz last week, and after the final loss he said that he felt tormented by the injury.
- I had pain.
I have trouble breathing.
I do not know if there is anything on the rib, Nadal said after the final loss.
Now it will be a battle against the clock for him to be ready for the French Open in May.
The Grand Slam competition, which Nadal has won 13 times, starts on May 22.