The Celtics may say they still have interest in re-signing Ray Allen, but they have secured some interesting insurance at the shooting guard spot along the way.

According to two league sources, the team has reached agreement on a three-year, full mid-level contract for former Mavericks guard Jason Terry. Under the provisions of the mid-level exception, Terry will make approximately $5 million in the initial year of the contract.

Terry, 34, was the NBA’s Sixth Man of the Year during the 2008-09 season. A year ago, Terry averaged 15.1 points per game while shooting 43 percent for the field in 63 games for the Mavericks. Nicknamed “the Jet,” Terry has been known over the years as a wiry defender and capable transition player. His spot-up style would work nicely with Rajon Rondo’s drive-and-dish game.

In his 13-year career, Terry is averaging 16.1 points and 4.7 assists per game. He is a career 44.8 percent shooter. He also shoots 85 percent from the line.

One of the sources stressed that the Celtics remain interested in Allen, who has already talked with officials from Memphis and Minnesota this week, and plans to meet with Miami on Thursday and the Clippers on Friday.

The possible combination of Terry and Allen would give the Celtics a deadly mixture from downtown, though neither would likely start ahead of Avery Bradley.

There would also be the question of playing time. Allen, who looms as a likely starter for the Clippers, appears to want a more prominent role than the way Doc Rivers’ rotation may be unfolding.

Terry’s emergence as a Celtic also calls into question the team’s commitment to Mickael Pietrus, who is still waiting for a call from the team.

According to Pietrus’ agent, Bill McCandless, the tough-defending swingman has, in the meantime, been contacted by four other teams, including one with stronger interest than the others. Pietrus has talked directly with officials from two of those teams, including one coach.