"F---ing sick and tired of being babied," Embiid wrote on his Instagram account.
Embiid has been sidelined since March 28 after suffering a broken orbital bone and concussion in a collision with teammate Markelle Fultz. Embiid underwent surgery to repair the fracture.
When asked about the Instagram post, Embiid told ESPN's Ramona Shelburne: "I promised the city the playoffs and I'm not on the court and I may not be on Thursday either. I wish more than anything that I was out there. I just want the green light to play."
Sixers coach Brett Brown said there is no specific timetable for Embiid's return.
There are still a few medical hurdles for Embiid to clear as he returns from surgery, sources told ESPN. The recovery is a process of ramping up to different stages of activity.
Internally, there is optimism that Embiid will return when the series is in Miami, though it's unclear if he will play in Game 3 on Thursday, according to sources.
Brown said Monday that he did not have a problem with Embiid showing frustration about his absence.
"He just wants to play basketball. He wants to be with his team. He wants to play in front of the fans and he wants to see this through," the coach said after the Sixers' 113-103 loss. "And when he's not able to do that, he gets frustrated, and we respect his frustration. It's born out of competitiveness, and it's born out of him wanting to be with his team."
Brown added that he did not want to discuss the specific medical issues that have kept Embiid from making his return. The coach said earlier Monday that Embiid had not yet been cleared to take contact during workouts.
Embiid, who averaged 22.9 points, 11.0 rebounds and 1.8 blocks in 63 games in the regular season, has cleared the NBA's concussion protocol. Philadelphia lost Monday for the first time in Embiid's 10-game absence.
The Sixers had won 17 consecutive games before losing to Miami in Game 2 at home.