LONDON (Reuters) - Three-times French Open champion Gustavo Kuerten knows what it is like to have a career plagued by injury but believes Rafael Nadal will come back strong from his latest ailments.
Spaniard Nadal has not played since a shock defeat by Nick Kyrgios at Wimbledon, since when a wrist problem and a troublesome appendix have sidelined the former world number one.
Nadal, whose ninth French Open title in June was a rare highlight in a difficult year, will return to action after Christmas and Kuerten expects the 28-year-old to be challenging for more grand slams in 2015.
"It's worrying for all of us who love watching him when he's injured but then he keeps surprising us," the 38-year-old Kuerten, forced to retire in his prime due to hip problems, told Reuters.
"He turned it around last year and finished up as the number one again. Anything is possible for Rafa, but it depends on his physical condition and the level of Novak (Djokovic)."
Kuerten does, however, urge caution.
"His style has a massive impact on the body, it's based on his physical performance a lot," said Kuerten, affectionately known around the world as "Guga".
Although it may be asking a lot for Nadal to pick up the pace quickly enough to challenge for the Australian Open -- the year's first grand slam -- Kuerten believes he will be firing on all cylinders for next year's claycourt season.
"Rafa thinks that is his territory," he said. "I think even when he's 95 years old you won't be able to keep him down. He's like from another planet at Roland Garros."
Kuerten, who finished 2000 at the world number one after beating Pete Sampras and Andre Agassi back-to-back at the ATP Tour Finals in Lisbon, retired in 2008, finally admitting defeat to the injuries that began to torment him shortly after his third Roland Garros title in 2001.
He said players were now less likely to suffer the same fate due to better protection by the ATP.
"The late 90s and 2000s it was the extreme killing time of tennis players," he said. "You look at (Marcelo) Rios, myself, (Magnus) Norman, even Marat (Safin). They pushed the players so hard that they started to break one after the other.
"We had to play nine obligatory Masters Series, four grand slams and then the season carried on until December, one month extra, and the Masters Series finals were best of five sets.
"The ATP realised that it was too much and not fair and they are getting the schedule fixed."
Kuerten, ever popular in Brazil where he runs tennis schools for disadvantaged children, has no regrets, however.
"For sure my best years in tennis didn't happen," he said. "But my life in tennis was great and it would be unfair to ask for more."
Editing by Ed Osmond