File this under "well that's odd." Though I'm not sure it is a lot to worry about.
The Celtics are not taking it as a major issue, but the team is still hoping to straighten things out with Rajon Rondo after his decision to stay in Los Angeles and not accompany the team to Sacramento for Saturday’s game. While some were displeased by the move, for which Rondo did not receive official permission, others pointed out he was not scheduled to play in the game anyway (on the second night of a back-to-back), and that he may have simply been making some assumptions based on precedent. Multiple sources say he remained in LA for a birthday celebration. He turned 28 on Saturday.
Rondo brushed off questions about it saying that it was taken care of already. Ainge said that he would look into it and talk to Rondo when they got back to Boston. Chances are that we'll never hear another update on it (Bulpett mentioned that it is possible he'd be fined).
To play devils' advocate, I suppose this could be some kind of minor blow-back from Rondo over seeing his name in trade rumors once again. Or maybe some in the organization think this is an example of poor leadership and not showing support for his teammates.
Still, it kind of sounds like a miscommunication to me. Rondo had a scheduled day off to rest his knee, the team had traveled without him (left him home) on another scheduled day off this month, you can see how he'd assume that this would be fine. Sounds like they just need a clearer policy for asking for days off.