Rumors about Phelps reversing his retirement picked up steam after he entered the drug-testing pool for international competition before the Nov. 6 deadline.
He was sighted recently at the Arena Grand Prix in Minneapolis, cheering on his roommate Conor Dwyer, who won a gold medal for the 4x200 freestyle relay at the 2012 Olympics.
But that doesn't mean Phelps is in the shape that helped him win an all-time record 18 gold medals and 22 total medals in his Olympic career.
"[Dwyer] swims the [400-meter IM], that's too long. I can't do that. I literally don't think if I jumped in the water right now, I could finish a 400."
Phelps was appearing with his mother, Debbie, at a fundraiser celebrating moms for the Education Foundation. Debbie Phelps has previously said she "would love to go to Rio," referring to the 2016 Olympics in Rio De Janeiro.