The number of known coronavirus cases within the NBA doubled to 14 on Thursday, when Marcus Smart of the Boston Celtics pleaded with people to take social distancing more seriously and the league ordered all teams to shutter their training facilities indefinitely.

Smart revealed that he tested positive and the Los Angeles Lakers said two of their players tested positive as well, bringing the number of players who have acquired the virus to 10. The Philadelphia 76ers said three members of their organization tested positive and the Denver Nuggets said someone within their franchise was positive as well.

The 76ers and Nuggets did not say if the affected people were players, coaches or other staff.

“I’ve had no symptoms and I feel great,” Smart said on Twitter. “But the younger generation in our country MUST self distance. This is not a joke. Not doing so is selfish. Together we can beat this, but we must beat it together by being apart for a short while.”

The league wants its teams to keep distance as well. Earlier Thursday, the NBA sent a memo to teams telling them to close their training and practice facilities to all players and staff — plus recommending that players “take aggressive measures to avoid contact with others and remain home as much as possible, leaving only for essential activities.”

Smart said he waited five days for his test results.

“I’ve been self-quarantined since the test, thank goodness,” Smart tweeted. “COVID-19 must be taken with the highest level of seriousness. I know it’s a #1 priority for our nations health experts, & we must get more testing ASAP.”

Smart’s comments and the other positive-test revelations came hours after the NBA’s memo, a copy of which was obtained by The Associated Press, was sent Thursday afternoon. The league told teams that it was going to more-stringent policies “in light of the rapidly-developing coronavirus situation, and consistent with evolving advice from health experts regarding how to promote individual and public health while minimizing the spread of the virus.”

As recently as Monday, the NBA was telling teams that individual workouts could take place at team facilities using what the league called the “one player, one coach, one basket” rule. Now, that’s not even permitted. If players are going to work out during the league’s shutdown, they’ll have to do it at home or some other private facility. Public facilities, like gyms or college courts — many of which are closed anyway — aren’t permitted to be used by NBA players under the league’s coronavirus policy.

Essential activities, by NBA definition, include buying food, medicine, or other necessary supplies; obtaining critical medical services; providing necessary care for a family member in another household; or attending to some other emergency.