Maybe it shouldn't be a surprise, but the Celtics-Clippers trade talks have hit another bump in the road. Here's the latest:

As the Los Angeles Clippers and Boston Celtics seemingly inched closer to an agreement that would bring an end to their on-again, off-again negotiations and finally send both Celtics star forward Kevin Garnett and coach Doc Rivers to Los Angeles, sources close to the process said Thursday that a hurdle at league level threatens to scuttle the talks yet again.

Sources told ESPN.com that it has been communicated to both teams by the league office that the NBA has questions about the proposed transactions involving Garnett and Rivers and the appearance that they are connected.

The teams awoke Thursday, sources said, close to an agreement on separate transactions that would land Garnett and Rivers in Los Angeles. The first is a proposed one-for-one player swap that would send Clippers center DeAndre Jordan to Boston for Garnett, who would waive his no-trade clause to clinch the deal. The second move would require the Clippers to convey two first-round picks to Boston as compensation for the Celtics agreeing to let Rivers out of the three years and $21 million left on his contract.

League rules not only prohibit coaches from being formally "traded" but likewise prevent teams from making any trade or free-agent signing with contingencies or side deals attached. So it is incumbent on the Celtics and Clippers to convince the league office that these transactions would be made independently.

"We know when teams break up trades to get around the CBA," NBA commissioner David Stern said Thursday on "The Herd with Colin Cowherd" on ESPN Radio.

One source with knowledge of the talks told ESPN.com on Thursday that the Celtics and Clippers have been negotiating for days knowing that league rules could well prohibit the transactions from going through.

Another source connected to the talks said Thursday that the Celtics and the Clippers, in the wake of ESPN.com's report about the league's concerns, have begun discussing alternative trade constructions to address any potential misgivings from the NBA.

* Rapid reaction: Given that the trade of an under-contract coach is such a rare occurrence, the league is clearly trying to prevent opening any sort of CBA loophole that teams could exploit in the future in terms of player/coach movement. It's hard to believe the league has any issue with the individual transactions themselves (making Kevin Garnett for DeAndre Jordan one transaction, and Doc Rivers for two first-round draft picks another, doesn't skirt any transactions rules). But the fact that the deals appear contingent on each other, and would be made concurrently, make it difficult for the league to rubber stamp the swap. Here's the full quote from Stern on ESPN Radio's "The Herd" earlier today: "I would say that, if we know that what the parties really want to do is one [trade and] they are going to break it into two for purposes of trying to avoid the restrictions that the collective bargaining agreement places on it, we know how to deal with that." In short, the Celtics and Clippers have to find a different way to make this happen. Let's see where things go from here. -- Chris Forsberg