Former US Olympic Swimmer Michael Phelps, right, and Brazilian soccer legend Pele eat sandwichs at a Subway restaurant, during a event organized by Subway, on Wednesday, Dec. 4, 2013 in Sao Paulo, Brazil.  [Photo/icpress.cn]

SAO PAULO - Retired swimming legend Michael Phelps has left open the possibility of competing at the Rio 2016 Olympic Games.

The 18-time gold medal winner earlier this year ruled out a comeback but he suggested a possible change of plans during a promotional visit to Brazil on Wednesday.

"I don't know what's gonna happen in three years. I don't even know what is gonna happen tomorrow," Phelps told reporters.

"I've said 100 times if I feel like coming back ... I could. But I'm not saying I am going to."

Phelps' coach Bob Bowman raised speculation of the star's possible return last month by confirming the 28-year-old signed up for drug testing in May, allowing him to compete as early as March.

Phelps is the most successful Olympian in history with 22 medals. He retired last year after winning four gold medals and two silvers at the London Games.