Miami - An inevitable clash of culture and personalities has led to an apparent split between longtime ATP friends and hot rivals Roger Federer and Rafael Nadal, with the Spaniard recently resigning his position at vice-president of the influential Players' Council.
The volatile Nadal who wears his heart on his sleeve on and off the court and who has for years been nothing but admiring of ice-calm Swiss Federer, seems to have finally had enough.
With issues bubbling in the men's game including the basis of the ranking system, the distribution of prize money and the length and weight of the annual schedule, cracks between the pair who ruled on court for almost a decade before the 2011 emergence of Novak Djokovic have finally hardened.
While neither man has made a public pronouncement on the issue - Federer still leads the Player Council - the rifts have been emerging for some months.
While in the past Nadal even visited Federer at the hometown Basel event, the pair are no longer presenting a solid front - with the clashes of ideas said to be most pronounced behind the closed doors of ATP meetings.
Federer was firmly against Nadal's hope of changing the ranking system from a one-year span to twice that length - which would have helped him hang onto his own standing for longer. The third-ranked Swiss said that such a change would make it harder for younger players to break through onto the ATP.
In addition, Federer's quiet authority helped to ensure that former Wimbledon winner Richard Krajicek was not selected as new boss of the ATP, with the job going to Australian executive and longtime insider Brad Drewett, a more suitable candidate in the eyes of the Swiss.
Then there was the matter of a summer exhibition which Nadal's people wanted to stage with Federer at Madrid's Bernabéu stadium. The idea died on the vine when the two sides could not agree on a July date amid the crowded tennis calendar.
While Nadal has always been more than complimentary towards Federer - and vice-versa - it appears the limits of friendship have been reached and breached.
"We have completely different characters, so from off the court I have my character. It is important to look around and learn from everybody," said Nadal. "I can't tell you something specific about what I learn about Roger because I have my character.
"I learned a lot more from the people who are close to me: my family, my friends."
While Federer personifies the smooth corporate face of the game - a sponsor's dream - Nadal is more rough-hewn, although with multi-million dollar contracts in his pocket as well.
While natural diplomat Federer counselled calm during the heat of the disfunctional US Open last autumn when rain washed away four days of play and strike talk was heavy in the air, Nadal came out with guns blazing on players' rights.
Nadal said players are being used. "We don't feel protected. Players are part of the show, and we should have a voice. We are working hard, and we want to feel good when we are at a tournament."
Nadal, a 10-time Grand Slam winner, said that players "cannot accept" such conditions.
"We have to be together - that's the only way to change things," he said. "I have a big desire to play the US Open, but I don't feel safe to play in rain."
The current sticking point for players is the size of the prize-money payout compared to total Grand Slam budgets, with players led by Nadal among other agitating for a bigger slice of the pie.
In Australia in January, reports indicated that strike action was discussed for this year, with talks obviously going nowhere among a group of more than 100 individual contractors, each with his own agenda and career to deal with.