The NBA sent out a memo Thursday afternoon stating that, starting Friday, all 30 NBA teams must close their practice and training facilities to players and staff until further notice, sources told ESPN.

Thursday's memo was an update on ones sent out by the league earlier this week, in which it outlined how teams should handle players and staff coming in and out of their buildings as the league remains on an indefinite hiatus due to the coronavirus and how players and coaches should be isolated from one another to limit potential spreading of the virus among team members.

Now, though, players are both not allowed to use team facilities or, as laid out in a memo sent out by the league Sunday night, work out at any non-team practice or training facilities -- essentially leaving players no choice but to attempt to work out at home as they, and the league, try to figure out what the next steps will be.

The league continues to recommend that players remain in their team's home market and to leave their homes only when they absolutely must, such as to go grocery shopping or get medicine. A ban on players leaving North America remains in effect.

Because of the changes in the rules, teams are now not allowed to engage in group or individual workouts with their players, though teams are allowed to provide workout materials for players to use at home if they want to. Teams are also encouraged to check in with their players daily electronically.

Since suspending its season indefinitely on March 11, the NBA remains uncertain when it will return to action. Commissioner Adam Silver, in an interview with ESPN's Rachel Nichols on SportsCenter on Wednesday night, said he isn't ready to contemplate the possibility of the remainder of the season being canceled.

"I'm optimistic by nature, and I want to believe that we're going to be able to salvage at least some portions of this season," Silver said. "I would say we have done new and creative things in the past. We experimented with this year's All-Star Game with a unique ending. We've talked about play-in tournaments for going into the playoffs. There may be other things we can do with the format.

"I have heard from a lot of our players. It's only been, it's actually been less than a week. They're going stir crazy, they want to play, they want to compete. Players, as you know, I mean, unlike a lot of us in our positions we can just go back to what we were doing, but every player is fighting something that's unwinnable, and that's the aging process. So a lost year or lost portion of a season in their careers is very different from other people, so we're gonna try by every means we can to play basketball again, but I say that the safety and health of our players is first, and our fans, which is why I don't want to speculate more on that.

"That will be the condition upon which we can play: When public health officials give us the OK."