Andy Murray's coach Ivan Lendl on Monday welcomed Rafael Nadal back from a long injury layoff, but said it was too early to judge whether the 11-time Grand Slam winner would be at his best.
The Spaniard swept to a straight sets victory over countryman David Ferrer at the Mexican Open on Saturday, his second title in three events since returning from a seven-month absence with a left-knee injury.
The so-called 'Big Four' -- Novak Djokovic, Andy Murray, Roger Federer and Nadal -- are set to be reunited at the Indian Wells Masters later this week, but Lendl cautioned against reading too much into the 26-year-old's comeback wins.
"He's a great champion and it's always sad when someone like that gets injured and cannot play. So it's great to have him back," Lendl said.
"As far as how it affects anyone's chances -- well he's a great competitor. It's a little bit early to judge. But there are many more tournaments to come before the French (Open) and before Wimbledon.
"You cannot underestimate Roger, Novak has been playing well, and Rafa -- we'll see how he's doing."
The Czech-American great said the immediate effect of Nadal's return would be to tournament seedings. The Spaniard's likely fifth seeding in line with his post-injury ranking meant he would meet a fellow top player in the quarter-finals.
Lendl said it would be tough for players outside the Big Four, such as sixth-ranked Tomas Berdych of the Czech Republic, to win a major this year.
"The problem anybody has outside of the top four is that they have to beat three, or if not three then at least two (of the Big Four), to win a Grand Slam title.
"They have to beat somebody in the quarter-finals then semi-finals then finals to win a Grand Slam title. And I don't believe that has been done yet by anybody beating all three."
Argentine Juan Martin del Potro was the last player outside the Big Four to win a Grand Slam with his US Open win in 2009.
Lendl said US Open and Olympic singles champion Andy Murray would be looking to improve on his performance last year at Indian Wells, where he crashed out in the second round.
Lendl was speaking at a press conference ahead of the BNP Paribas Showdown in Hong Kong, where he will play his ex-rival and fellow great John McEnroe in an exhibition match later Monday.