'My bad' says Roger Federer as he says sorry for blunder over Bernard Tomic's ranking

Federer, a 17-times grand slam champion, had said at the Brisbane International the 23-year-old Tomic, touted as one of the up-and-coming generation of men's tennis, was "far away" from reaching the top-10.

Tomic, the highest ranked Australian at 17, took umbrage at the remarks and then told reporters at Melbourne Park that as far as he was concerned Federer was "nowhere near" the level of world number one Novak Djokovic.

The Swiss, however, said on Tuesday after he comfortably accounted for sixth seed Tomas Berdych to move into the Australian Open semi-finals, that he had not realised Tomic was as highly-ranked as he was and all he meant was he had the talent, but like many others needed to keep working.

"To be quite honest, when I walked out of the press room (in Brisbane) I thought I was somewhat tough, but at the same time I was fair because I said nice things about him," Federer said.

"But then I checked his ranking. 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.

"That was my bad, to be honest."

Tomic, who lost to Andy Murray in the fourth round on Monday, had clearly been stung and hit back at Federer, saying how the Swiss was "nowhere near Djokovic right now".

Unsurprisingly, then, Federer repeated his assertion that making the top-10 and staying there was a real battle for any of the next generation of players - and one which requires huge amounts of hard work as well as talent.

"It's a big difference top-10 for a week or for a year or for multiple years, and getting there is not easy," he added.

"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."

The Swiss added he thought Tomic's controversial compatriot Nick Kyrgios should also be aware of trying to win over the public after a testing 12 months.

Kyrgios is still playing under a suspended ban for an off-colour remark to Federer's compatriot Stan Wawrinka last year and he alienated his home fans in Melbourne with more heated outbursts in his third round loss to Berdych.

Federer, who practiced with Kyrgios ahead of the then 19-year-old's Wimbledon quarter-final run in 2014, added the world number 30 had "sick power" and could also go a long way, if he could develop better control on court.

"I think he's doing okay now, better now. He needs to, obviously, for what happened last year," Federer said.

"I just think the next couple years are going to be so crucial for him, and I just hope he's aware of that fact. Otherwise the train leaves the station and you're not on it."