Embiid and Simmons were exposed to their personal barber, reports The Athletic's Shams Charania. That barber then returned another positive test result, confirming the diagnosis, sources told ESPN's Adrian Wojnarowski.
The two 76ers stars traveled to Atlanta individually on private planes and were not exposed to other players or individuals due to the league's mandated quarantine, according to Charania.
The NBA has also announced Embiid and Simmons will no longer be required to conduct required media availabilities before the game, according to The New York Times' Marc Stein.
Embiid, a four-time All-Star, was named a starter for Sunday's event after co-captain Kevin Durant picked him to play on his team. Simmons, who was on pace for his third All-Star appearance, was selected by LeBron James after NBA coaches voted him in as a reserve.