J.R. Smith has knee surgery, out 12-16 weeks
The knee was said to be bothering Smith for a while, and it "gradually worsened" as time went on. A tweak during the Knicks' series against the Indiana Pacers could have been what aggravated the injury to the point that it needed surgery.
The recovery timetable given by team doctors is 12-16 weeks. As long as Smith doesn't take the full extent of that timetable, he should be ready for the start of the regular season. That being said, he is unlikely to get any preseason work in (training camp, preseason games, etc.), and no one wants to see a rusty J.R. Smith hoisting up shots when the regular season rolls around.
Head coach Mike Woodson frequently preaches strong conditioning to his players, so Smith may not be in game shape when the season starts, as far as Woodson is concerned.
Easing Smith back into heavy minutes (he averaged a career-high 33.5 last season) may take a few games, so that could very well mean more minutes for the Knicks' other wing players early in the year. Iman Shumpert is likely to play a big role throughout the course of the season, and could be called upon to play even more minutes until Smith is ready to get back to that 33.5 per game mark. Rookie Tim Hardaway Jr., who was expected to be very slowly eased into the rotation, could also see some significant playing time. Hardaway Jr. very well may be the biggest beneficiary (as far as extra minutes) from Smith's injury.
Though the injury doesn't sound good and the timetable is near a max of four months, Smith has never had knee issues in the past, which hopefully means that he will return to his pre-injury form when he recovers. At the age of 27, there is not much to worry about in the long-term for Smith. He has a good shot at being ready by the start of the regular season, and though his conditioning may limit him early on, he should be just fine.