Nick Kyrgios has earned high praise from tennis legend Roger Federer after another encouraging grand slam showing at the French Open.

Kyrgios, at 19 the youngest man in the draw, was outclassed but far from disgraced in a 6-3 7-6 (7-1) 6-3 first-round loss to eighth seed Milos Raonic on Sunday.

The Canberra teenager spent a week training with Federer in Zurich as part of preparations for Roland Garros and he made a strong impression on the 17-time grand slam champion.

“I really like his game,” Federer said of Kyrgios after the Swiss fourth seed opened with a comfortable 6-2 6-4 6-2 win over Slovakia’s Lukas Lacko on Sunday.

“I think he’s very open to trying out things, going for the big shots.

“I think he’s got really great potential.”

But Federer also urged the 193cm teen not to let his talent go to waste.

“I think he’s strong physically but clearly he needs to keep working hard now to make sure he makes the next move and he’s solid for five hours, solid for two weeks, solid for one year, all that stuff,” Federer said.

Former top-ranked junior Kyrgios has struggled in the past with his fitness and admits he’s still some way off being physically ready for the rigours of the men’s tour.

He upset Czech veteran Radek Stepanek at Roland Garros in his grand slam debut last year, and also won his first round match at the Australian Open, but struggled to back it up in second round matches.

Kyrgios felt his performance against Raonic, where he had his chances and led 4-2 in the second set, showed he was already making significant progress.

“I was getting to a lot of balls I wasn’t going to get to last year,” Kyrgios said.

“I was feeling fine physically out there so I can take away that I’ve done a lot more hard work as well.”

Sunday’s match was more than likely the first of many between the pair in the coming years.

At 23, Raonic is the youngest player in the top 10 and he believes Kyrgios can become a feared player on the tour.

“He’s very capable, he’s talented, especially off the forehand side. He can surprise you in many ways,” Raonic said.

“I haven’t been really on tour that long that I can tell you, seeing a lot of guys come up, what really the big differences are.

“But there are definitely weapons there that can make a lot of players feel uncomfortable.”

Kyrgios will compete in the mixed doubles at Roland Garros alongside Swiss teenager Belinda Bencic.