Sounds like Bradley's rib injury wasn't healing as fast as they would have liked, so they got another X-ray to make sure there wasn't a fracture.
Celtics Insider | Boston Herald
The Celtics were able to breathe a little easier today with the news that a second X-ray raken of Avery Bradley's bruised ribs was negative. Though Bradley didn't take part in today's practice open practice for the families of New England Bapstist Hospital employees, he is expected to travel with the team to Detroit for tomorrow night's game against the Pistons, followed by a game in Cleveland on Tuesday.
So will he play tomorrow? Doubtful.
Bradley 'doubtful' vs. Pistons
Celtics guard Avery Bradley will travel with the team to Detroit but is "doubtful" for Sunday's game against the Pistons, according to Doc Rivers.