Andre Agassi told ESPN's Rick Reilly he was "out of line" and apologized for poking fun at Pete Sampras during a charity match last week.
Longtime rivals Agassi and Sampras were wearing microphone headsets during the match, and the crowd at Indian Wells Tennis Garden in California got an earful during an exchange that started lighthearted but turned testy.
At one point Sampras mimicked Agassi's pigeon-toed walk, which drew laughs from the crowd.
Then Agassi chided Sampras for being stingy. In Agassi's autobiography, "Open," released last fall, Agassi criticized Sampras for being a poor tipper.
Sampras responded with a high, hard serve that forced Agassi, who was teamed with Rafael Nadal, to duck.
Both Agassi and Sampras were smiling, but neither showed up at the postmatch news conference.
Agassi told Reilly that he feels "sick about it."
"It was out of line," Agassi said Monday. "It was inappropriate. The night was on fire. We were all having fun. I was trying to be comedic. I only had a split second to make a decision. I went for it and it fell flat. I was trying to get past it, but Pete didn't really let me get past it. He didn't really roll with it. I've texted Pete to ask him if I can apologize in person."
"The joke fell flat and I'm sorry," he added. "My hope was that the night was still enjoyable."
Nadal was asked about Sampras and Agassi after his Monday night match.
"Everybody told me after the match what's happened, but during the match, you know how fast Americans speak, and I am Spanish. I didn't understand nothing," he said.
He said he felt no tension between them either on or off the court.
A capacity crowd of 16,100 filled the stadium for the Hit for Haiti fundraising exhibition Friday night put together by Oracle founder Larry Ellison, who purchased the tournament at Indian Wells in December.
The event helped raise $1 million to aid relief efforts in the earthquake-ravaged island nation.
Information from The Associated Press was used in this report.