I hesitated to even bring up that scenario, as it NEVER happens, especially not to players of Neal's caliber.
Good players tend to stay with the team that drafted them for 7-9 years, because after their rookie deal is done, they're RFAs. So even though they'd probably like to leave their teams if they're bad like the Raptors or Kings, they'd rather get a big contract. So they just accept a max extension from their current team, as that team will probably match whatever deal another team gives to a player.
If the good player REALLY wanted to leave his team as soon as possible, he'd just sign his QO when free agency starts. That means he'd have to play for his current team one more year, but after that, he'd be unrestricted and could sign with the team of his choice without fear of his current team matching. He's also gain a de factor no-trade clause, which would allow him to choose whatever team he wanted to go to if his current team wanted to get something from him.
You never see this maneuver, though, because it's financially and socially risky. The player gives up a lot of guaranteed money and really earns his team's ill will . It makes for a terrible year for everyone. However, when you hear players like Eric Gordan beg Phoenix not to match his offer sheet, you have to laugh. He could have just signed his QO and picked his place his season. Instead, he's stuck in New Orleans or wherever the Pelicans decide to ship him for the next three years.
As far as Neal goes, however, that means nothing. If he REALLY wanted to leave the Spurs, they'd just let him go. The only player they'd keep against his will (for more than just one season) is Leonard. Neal just isn't worth the struggle.