John Antil, an assistant professor at the University of Delaware's Lerner College of Business and Economics who studies celebrity endorsements, called Phelps' statement "excellent."
"One of the first lessons we've learned from crisis management is to be honest. Next is to show regret," Antil said. "I would say that that statement is probably as good a statement as he could make. He didn't deny it. He gave a plausible reason: Young people do this. ... He didn't say, 'I didn't inhale.'"
All professional athletes have clauses in their endorsement contracts for behavior, Antil said, making it relatively easy for a company to drop Phelps for the impropriety.
"If Speedo decides this is a big deal, it's an easy way to get out of their contract," Antil said. "But I strongly suspect that's not going to happen."
Although the immediate response from Phelps' camp was strong, follow-up will be key, Antil said.
"If he goes on the Letterman show or some talk show, they're probably going to talk about it, and that's a good thing, and then you hope the press forgets about it and leaves him alone. My guess is because of what happened and his age and his degree of popularity, people are going to give him a break."
Phelps' mother, Debbie, a principal at Windsor Mill Middle School, didn't return calls from The Baltimore Sun seeking comment.
The Associated Press contributed to this article.