Arthur Staple at Newsday
reports that in order to be bought out Chris Drury has to be medically cleared by the June 15th start of the buyout period, or the Rangers can't buy
him out. It is highly unlikely for this to be an actual issue as Drury did return for the final game of the regular season and participated in a limited role during New York's playoff series against the Capitals. There is also a grievance process if the club and player disagree on the ability to play, but I certainly doubt that it will come to that between Drury and the Rangers. Drury likely wants to continue playing, if his knee will allow it, so taking the buy out and looking to catch on somewhere else is his best course of action right now.
If Drury fails to be cleared and the Rangers cannot buy him out, then they could have cause to put him on long-term injured reserve (LTIR) which would allow the Rangers to exceed the salary cap by the amount of his salary next season.