Do not to expect to see Chris Bosh on the court anytime soon. According to the Miami Herald's Barry Jackson, Bosh isn't trying to influence the Miami Heat to waive him right away, and any comeback attempt will likely wait until the 2017-18 season.
At the moment, an attempted comeback next season is considered more likely (with another team, if he can find one to clear him medically), though it's impossible for Bosh or anyone to know how soon he can play.
Bosh is making no attempt, at this time, to force the issue and make the Heat release him.
The players union would consider getting involved only if Bosh decides in February or March that he wants to try to play immediately, and the Heat hasn't yet released him.
Regardless of all of this, it's questionable if any team doctor will clear him. Pat Riley already has said that the Heat is no longer working toward a Bosh return to the court.
The National Basketball Players Association is reportedly monitoring Bosh's situation, but there's little to be done right now. It is extremely unlikely that any team would clear Bosh to play -- recurring blood clots led to him not only failing his physical with Miami, but team president Pat Riley declaring that his career with the Heat was "probably over."
Bosh has said he still wants to play in the NBA. There is no timeline for that, however, and given what he has been through, it is possible that he's played his last game.