Shaquille O'Neal at practice

WALTHAM, Mass. -- Boston Celtics center Shaquille O'Neal, who suffered a right calf sprain April 3 against the Pistons, was back on the court briefly Thursday before the start of Boston's practice session at the Sports Authority Training Center at HealthPoint.

He did not address the media, hoping to test his calf the next couple days before that happens.

O'Neal got up some shots, then retreated to the locker room with his teammates to watch film. Celtics coach Doc Rivers said his team will simply hold a walkthrough Thursday as part of on-court activity before ramping up Friday, which will provide O'Neal's first real test with any eye toward getting him back on the floor for Game 1 against the New York Knicks on Sunday night.

O'Neal was out from Feb. 1 to April 3 with an Achilles injury. His return lasted a mere six minutes before he suffered the calf strain.

Rivers remains confident O'Neal will be ready to go when Boston tips off postseason play.

"I do [think Shaq will play in Game 1], I can't guarantee that," Rivers said. "He's going to do a little bit today. We're not going to do enough -- we're going to walk through stuff -- but [Friday] and [Saturday] are the big days for Shaq. He's going to try to get through practice and see what we can do."

Chris Forsberg covers the Celtics for ESPNBoston.com.