Tennis: Stan Wawrinka believes Roger Federer on course for world No. 1 ranking

Miami (AFP) - Roger Federer's comeback from injury has been so successful that his compatriot Stan Wawrinka believes he can become the oldest world No. 1 in history at the age of 35.

Federer beat Wawrinka in the final of Indian Wells on Sunday for his second win of the year following his triumph in the Australian Open - his 18th grand slam title and his first in four and a half years.

Those wins have propelled the Swiss master to sixth in the world as he makes excellent progress aftera six-month layoff caused by a knee injury.

Compatriot Wawrinka believes that not only is Federer back in form but he is playing in a noticeably different manner that gives him a chance to return to the pinnacle of the rankings.

"He's playing really well, what is different maybe is he is playing closer from the baseline, preferring, using less his slice, he is using more top spin, putting more pressure all the time, returning better that's the difference I seem," Wawrinka said on Tuesday at the Miami Open.

"For sure he has a shot at No. 1, he has just won the first Masters final. For sure he has a big shot," he told reporters.

Andre Agassi holds the record for being the oldest player to hold the men's No. 1 ranking, at the age of 33.

"It is going to be interesting to see. Rafa (Nadal) is playing well also and we will see when Novak (Djokovic) and Andy (Murray) are back from injury, it is going to be really interesting for tennis fans," Wawrinka said.

Federer could face a strong challenge from old rival Nadal who is seeking his first ever win in Miami after losing in four finals at the Key Biscayne venue.

The Swiss, a winner in 2005 and 2006, is the only former winner in the field and is looking for a third sweep of Indian Wells and Miami titles.