Source: J. O'Neal likely headed to Celtics

In a perfect world, the Dallas Mavericks envisioned a center tandem of Brendan Haywood and Jermaine O'Neal.

Haywood remains in play, but O'Neal, an unrestricted free agent who played last season for the massively re-tooling Miami Heat, will probably choose to join the Boston Celtics after also considering Dallas and the Denver Nuggets, a league source said late Wednesday night.

Haywood's top two suitors are Dallas and Miami. However, if recent rumblings that LeBron James is leaning toward Miami to join Chris Bosh and Dwyane Wade come to fruition, the Heat won't have the cap space to sign Haywood outright.

Stay tuned, as in 8 p.m., Thursday, ESPN.