Andre Agassi believes that Roger Federer has “a lot more in him.”

Andre Agassi and Roger Federer’s careers mirror each other in the sense that both kept their levels high and accomplished a great deal at an advanced age.

At 32, Agassi won the 2003 Australian Open. At a similar point in his career, Federer defeated Andy Murray to win Wimbledon in 2012, his seventh title.

In 2005, a 35-year-old Agassi made it to the U.S. Open final where Federer, of all people, beat him for the championship. Similarly, a 35-year-old Federer—playing for the first time in six months—won the Australian Open for his 18th major singles title.

Agassi, an eight-time Grand Slam champion who won all four majors and a gold medal during his illustrious 20-year career, played Federer 11 times before retiring in 2006. The Swiss bested the American in eight of their 11 mee

In a recent interview with TENNIS.com—in which the Hall of Famer discussed his new online course. And offered thoughts on Nick Kyrgios—Agassi assessed Federer’s run in Melbourne and opined on what he believes lies ahead for the all-time great.

“It was a legendary run and performance, unquestionably,” the 46-year-old said. “It kind of lived up to the standard of his entire career, quite frankly. And as it relates to his ability, or possibility of continuing this kind of level, I’ve sort of left the business of predicting Roger Federer anymore. He no longer surprises me, but he continually impresses me.”

Ahead of the Australian Open, Federer said he’d like to play at least two or three more years. And he put that plan into action last week when he agreed to play the Swiss Indoors through 2019. He’ll be 38 when that partnership concludes.

“I would say, under normal conditions, for a human being the idea of playing at this kind of level for much longer is not realistic,” Agassi said. “But he has proven that wrong—he proved that wrong this January. So yes, I think he has a lot more in him.”

Federer, ranked 10th, is playing in Dubai this week, his first tournament since the Australian Open.