Asked Friday whether he was confident Allen will be ready for the Celtics playoff opener Sunday against the Atlanta Hawks, Rivers told reporters:
"I don't know if I'm confident or not. I don't know how to answer that."
Just one day before, Rivers was still unsure about Allen's status but seemed to have more confidence.
"It's a concern, that's all I can tell you. I don't know much more than that," Rivers said Thursday before Boston's regualr season finale against the Milwaukee Bucks. "I think he's probable - in football terms, isn't that the term they use when there's a chance more than 50 percent that he'll play? So let's put him at probable."
Allen did not participate during Friday's practice session but could possibly compete when the team has another workout Saturday.