Originally Posted by 156mphserve
I would bet that it's possible in every single sport that keep official results based rankings as long as the player hasn't gotten removed from the official rankings list via proper channels.
There are probably different contract requirements in team sports. You announce your retirement via press conference... great, good for you. If you don't show up to play the next game you are going to get fined by your team or the league... so you better file your retirement paperwork ASAP.
ATP just has a lax approach towards this particular bit of paperwork because it doesn't affect anything like it would if a basketball player retired. As has been stated, players still make the entry lists that they would've made if his name wasn't there, etc.