Free agent guard Jason Terry and the Boston Celtics are approaching agreement on a three-year contract, according to Marc Spears of Yahoo! Sports. But the Celtics shouldn't count their chickens just yet.

Marc Stein of ESPN reports that Terry is still expected to give the Dallas Mavericks an opportunity to counter the deal, which is expected to net Terry $15.7 million over the next three seasons.

Though the Mavericks like Terry, who was a crucial piece to their 2011 NBA championship run, matching Boston's offer isn't a given. Dallas has spent the past couple seasons maneuvering to open cap space, and re-signing Terry would take away some of their flexibility.

If Terry does end up landing in Boston, it would be a coup for the Celtics, who desperately need scoring. Terry could also relieve some of Rajon Rondo's ball-handling abilities.

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