The Brooklyn Nets and Hawks are engaged in ongoing talks on a multiplayer deal that would send several expiring contracts to the Atlanta for All-Star guard Joe Johnson, according to sources briefed on the discussions.

But sources told ESPN.com that the Nets have expressed concerns throughout the weekend that they're surrendering too much financial flexibility in the various trade proposals presented to date, which has the teams trying to make tweaks to push the deal through.

One big stumbling block, sources said, is Atlanta's insistence that Brooklyn include promising Nets guard MarShon Brooks in the trade to ensure that, in addition to shedding Johnson's hefty contract, it gets back at least one on-the-rise player.

Sources say that the Nets, furthermore, will only go ahead with this trade if they know that it helps convince Deron Williams -- this summer's No. 1 free agent -- to verbally commit to re-signing with Brooklyn when a league moratorium on new contracts is lifted July 11.

The most recent proposal, sources said Sunday night, would call for the Nets to send the expiring contracts of Jordan Farmar, Johan Petro, Anthony Morrow and Jordan Williams along with the signed-and-traded DeShawn Stevenson and a future first-round pick to Atlanta in exchange for Johnson.