The Celtics confirmed one player contracted COVID-19 on Thursday amid the pandemic, and Smart revealed his diagnoses via social media.
"I'm OK, I feel fine. I don't feel any of the symptoms," Smart, 26, said in a video posted to Twitter. "But I can't stress enough practicing social distancing and really keeping yourself away from a large group of people and just really washing your hands and help protect yourself. And help protect others by protecting yourself."
"I was tested five days ago and the results came back tonight, which were positive," Smart added in his caption. "I've been self-quarantined since the test, thank goodness.
"COVID-19 must be taken w the highest of seriousness. I know it's a #1 priority for our nations health experts, & we must get more testing ASAP.
"I've had no symptoms and I feel great. 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. Much love!!"
The Celtics said in a statement: "A player has tested positive for COVID-19. Testing was initiated because of exposure to a known positive case.
"The Celtics player, who is not exhibiting symptoms, has been in isolation for several days and will continue to do so while being monitored by team medical staff. The team is awaiting further testing results and will communicate them as appropriate.
"Taking steps to maintain the health and safety of everyone in our organization and across the NBA remains our top priority, and we will continue to work closely with health officials and the league in addressing this situation."