As he sat at home under quarantine after testing positive for the coronavirus, Marcus Smart would watch news coverage of the growing pandemic.

The Celtics guard, who showed no symptoms when the test results were revealed on March 19, saw the death toll mount and the number of seriously ill patients rise throughout the world on a daily basis.

“Scary,” said Smart, speaking on a video conference with the media this week from the Auerbach Center. “It was terrifying to actually watch on the TV, to hear about it.

“I was diagnosed with it and it could have been me that was affected differently. I could have been symptomatic. I could have been in certain positions that certain people were. It was scary because no one really knows the extent of this virus. No one really knows exactly what to do.”

The 26-year-old Smart had been tested on March 14, four days after the Celtics played their final game before the NBA suspended the season. Smart and his teammates were already quarantined after flying back home from Milwaukee on March 12.

“We took the precautionary measures before I even knew,” said Smart. “When the diagnosis came, I isolated myself even more, washed everything over and over each day. The good thing about it is my girlfriend bought everything before the outbreak. I was set in the house. I really isolated myself from her and my cousin. Took extra measures. You go overboard with it. You’re washing everything constantly. I drank more water than I’ve ever drank in my life.”

Smart recovered from the coronavirus in a short time and was on a plane with his teammates Wednesday, headed to Florida where the remainder of the NBA season will be played.

The Celtics will practice and scrimmage for the next three weeks before playing the Milwaukee Bucks July 31.

“I feel great,” said Smart. “I’m ready to rock and roll.”

Smart tested positive for the antibodies and donated plasma to the American Red Cross. The plasma can attack the virus and help others who have the coronavirus.

When the Celtics’ season is over, Smart intends to donate some more plasma when he gets back to Boston.

“It was a very humbling experience,” said Smart, “just to know that somewhere someone in this world is going to take my plasma and it could possibly help them save their life or give them a fighting chance. That was unique in that part.

“It was harmless and painless. I encourage everyone, if you had the antibodies, to donate. You don’t know whose life you might change.”

Since he was asymptomatic, Smart said he was “skeptical” when he first learned about testing positive. But he quickly took all the precautions necessary while in quarantine and paid close attention to the virus.

“For me, I was a little skeptical at first, especially when I got that call that I was diagnosed with it just for the simple fact you feel nothing,” said Smart. “That was just me. I heard other cases where people are really having trouble with the respiratory system and things like that or even people who had COVID and coming back with the antibodies and trying to work out and they’ve having complications and problems.

“For me, my mindset was I’d rather be safe than sorry. Even though I do have that skepticism, I’m going to take the safe way, really, really hone in on making sure I do my part of staying inside, washing my hands and keeping my distance from people because we don’t know what this is. It’s kind of hard.

“The skepticism from me comes how can I know what you’re telling me without seeing anything is true? Somebody just called me and told me, yep, you were diagnosed with COVID. Well, how do I know that? I haven’t seen any paperwork, anything. I don’t know what is going on in those labs. But I’d rather be safe than sorry.”

Smart, who is averaging a career-best 13.5 points and 4.8 assists in his sixth season with the Celtics, has sent out the message to young people that the virus is serious and should be paid attention to for the sake of others.

“In my age group, we feel a little bit of invincibility,” said Smart. “We’re young. We feel like we’re in the best shape of our lives and nothing can happen to us. That’s the scary part because all it takes is one guy to really open everybody else’s eyes. You don’t want it to even get there. You want to try to prevent that and I think us older guys, guys who’ve had COVID like me, really chew down on the fact of taking it as serious as possible.

“You might not take it as serious, but you’re putting other people at risk. You go out there asymptomatic and you don’t know and you go to your grandma or you go home to your kid, your wife who is pregnant. You don’t know because you don’t feel anything and you don’t need to get tested. Now you spread it and it’s out of control even more than what it is.”

Even though Smart has had the coronavirus and is feeling fit and ready to play the rest of the NBA season, he’s still unsure whether the illness will have a lingering affect on him.

“Who’s to say even now I have the antibodies, the virus is gone, how it’s going to affect me in the long run five years from now, things like that,” said Smart. “It’s a scary moment for us right now as a human race. We’re all trying to figure it out. Everyone is scared and confused.”