The Houston Rockets, as they've been telling teams all month, remain on course to trade disgruntled big man Omer Asik by Thursday, according to sources close to the process.

Numerous teams consulted by ESPN.com in recent days have said they are convinced the Rockets will indeed go ahead with a trade headlined by Asik before their self-imposed deadline of Dec. 19, with sources saying Tuesday that the Boston Celtics are increasingly active in the Asik talks.

As a result, the Celtics now are widely regarded as the strongest rivals to the Philadelphia 76ers in terms of the likely destination for Asik, with many rival executives expecting the final form of a trade built around the 7-footer from Turkey to feature at least three teams.

Omer Asik, right, has been unhappy in Houston since Dwight Howard arrived in July. AP Photo/Jae C. Hong

Sources have described the Atlanta Hawks as Houston's preferred trade partner because the Rockets came to the conclusion last month that, despite their attempts to placate Asik, they eventually would have to give in to the unhappy center's long-running desire to be moved in the wake of Dwight Howard's arrival in July. Yet it remains unclear, sources say, how interested Atlanta really is in parting with coveted forward Paul Millsap -- who's considered an ideal frontcourt complement to Howard -- in exchange for Asik.

Although sources say there has been dialogue between the Rockets and Hawks this week, it's believed that Atlanta officials are lukewarm on Asik. Asik is owed nearly $15 million next season thanks to a balloon payment in his contract that the Rockets inserted during the summer of 2012 to dissuade the Bulls from matching Houston's offer. Sources say, though, that such a high figure for a defensive specialist does not trouble the 76ers or Celtics, who have emerged as the two teams most frequently mentioned as landing spots for Asik.

Cleveland is another team that has been frequently linked with Asik the past several days, but sources close to the situation maintain the Cavaliers like the fit of Anderson Varejao in their frontcourt rotation better than Asik and thus are more likely to participate in such a trade as a third-team facilitator rather than as the team that winds up with Asik.

One possible scenario that has emerged, sources say, is a three-way trade in which Boston lands Asik, Cleveland absorbs the contract of Celtics forward Jeff Green and Houston scores no fewer than one of the future first-round picks it covets for surrendering Asik. Other players would have to be involved in such a trade to make the salary-cap math work, but it's the sort of trade that would fall in line with Cleveland's well-known focus on upgrading its options at small forward.

The Cavaliers pursued Green in free agency two summers ago before Green re-signed with Boston and, as ESPN.com reported Sunday, have shown far more interest recently in finding a new small forward than going ahead with the rumored Varejao-for-Asik swap.

There likewise are league sources who have maintained all month that the Rockets' plan to trade Asik by Dec. 19 -- as first reported by ESPN.com on Dec. 6 -- was hatched in part because of general manager Daryl Morey's confidence in being able to strike a deal with Philadelphia, where former Rockets assistant general manager Sam Hinkie is now running the Sixers' front office.

Sources say the prospect of acquiring center Spencer Hawes and at least one future first-round pick would be Houston's aim in a trade with Philadelphia, although it's believed the Rockets and Sixers also would require at least one more team to complete a deal. Hawes not only possesses a cap-friendly expiring contract valued at $6.6 million this season but also has the offensive skills and shooting range -- unlike Asik -- to be able to play alongside Howard as well as back him up.