Spanish tennis superstar Rafael Nadal has likened his recovery from a rib injury to a "roller coaster" ride after making a winning return in the Madrid Open Wednesday.

The 21-time major winner returned to action with a straight-set win over Serbia's Miomir Kecmanovic.

The Australian Open champion was playing in his first event since picking up the injury at Indian Wells in March but showed little signs of rust, cruising to a 6-1 7-6(4) victory.

"I leave the match very, very happy. You have to be sincere with yourself ... my preparation has not existed. You cannot expect great things at the beginning," Nadal told reporters.

"All trainings have had some up-and-downs, it's been a roller coaster. I have had better days, worse days.

"At the end of the day, the rib is a problem that limits your game a lot."

The Spaniard added that training had been difficult due to the nature of the injury but he was not worried about his lack of preparation ahead of the French Open later this month, where he will be bidding for a record-extending 14th title.

"There are injuries that allow you to do physical work, aerobic work. The rib has not allowed me to do anything ... but I'm not worried. I just think that every minute that I am out there on the court is something positive," the 35-year-old said.

"I don't have any pain in my rib. I had a little bit of pain at the beginning of the week, and then I went to get an MRI so they could check it, Friday or Saturday when I came here, and the image on the machine was good."

Nadal, a five-time champion in Madrid, will take on Belgium's David Goffin in the last 16 later Thursday.