Roger Federer apologised on Tuesday after he sparked a row with Bernard Tomic by upbraiding the Australian about his work-rate -- without checking his ranking first.

Federer told Tomic he had to work harder if he wanted to reach the top 10, prompting Tomic to point out that the Swiss great was also some way away from the level of top-ranked Novak Djokovic.

But Federer admitted on Tuesday that he made the comments thinking Tomic was still ranked at about 50th in the world. When he checked the rankings, he realised he had risen to 17.

"I didn't know his ranking was as high as it was, to be quite honest. I thought he was like 50 or 60 and he was top 20," Federer said.

"That was my bad, to be honest. But I don't check the rankings every day. I came from the off-season. I had no clue what was going on anymore."

"But I still believe it's a big difference top 10 for a week or for a year or for multiple years, and getting there is not easy.

"It's a lot of dedication, a lot of hard work. There's a lot of guys who have the potential right now, not just him. That's why I think it got brought up in many ways."

Federer also warned wayward Australian Nick Kyrgios that the next two years are vital to realising his huge potential on the tennis circuit after a rocky patch in young career.
The controversial 20-year-old has polarised opinion over his behaviour on and off the court, and he bowed out acrimoniously in the Australian Open third round against Tomas Berdych.

"I think he's a great player. I think he's enjoyable to watch. I know some people might not like it. I like it. He's got a lot of personality," the Swiss great said.

But Federer warned: "The advice I would give him, just that he's aware of the fact how important the next couple of years are. Otherwise the train leaves the station and you're maybe not on it.

"It would be a pity to waste talent and all that even more so in this day and age because I feel talent brought you further back in the day.

"Just talking about a guy who has talent and potential, I can't hear it anymore. Too many guys have talent. Too many guys are working hard. I don't believe in that very much any more."

Last year Kyrgios was handed a 28-day suspended sentence, which expires on February 24, for making a sexual reference to Stan Wawrinka's girlfriend.
Source :AFP