Andre Agassi has insisted that Kei Nishikori is "very capable of winning a Grand Slam" title.

The world number five showed impressive form throughout the 2014 campaign, despite losing in the final of the US Open to Marin Cilic.

However, regardless of that defeat in New York at the hands of Cilic, Agassi has seen enough from the Japanese player to suggest that he will win one of the four major titles in the near future.

"He was one match away from US Open. Probably the biggest reason for [not winning the title] was the physical wear and tear over the course of the tournament, and sometimes that's a bit unlucky," he told AFP.

"There is no question in my mind he believes he can win a slam. I've seen him play with that purpose. From a talent perspective, he's very capable of winning a grand slam. He's dynamic and incredibly fast."

During his career, which ended in 2006, Agassi won eight Grand Slams.