"Listen, he's just feeling better and he's closer. I don't know what he needs to show me," Rivers said after the Celtics' morning shootaround Friday. "He's not ready to play yet, but he's getting closer. The fact that he's getting closer, you bring him on the road."
The entire roster of the Celtics, who lead the best-of-seven series 2-0, made the trip.
During Wednesday's practice at the Sports Authority Training Center in Waltham, Celtics coach Doc Rivers said that O'Neal's ability to travel would suggest he might be able to play again as early as Sunday's Game 4 in New York.
"If he's closer to playing -- you know how we've done it -- if you see him on the trip he's really close," Rivers said Wednesday.
Later, Rivers added: "If he goes on the trip, that means we think he'll play that Sunday."
O'Neal appeared in 37 games for the Celtics this season, and has been plagued by injuries to the right side of the body, particularly the knee, calf and Achilles. The 39-year-old center has played only 5½ minutes since Feb. 1.
"I'm worried about getting him right and healthy," Rivers said. "There's no strategical game plan for not playing him. There's a medical game plan for not playing him and he can't play. Once he can play, he can play."
Chris Forsberg covers the Celtics for ESPNBoston.com. Information from The Associated Press was used in this report.