Scratch another item off Danny Ainge‘s to-do list. Multiple outlets are reporting, and WEEI.com has confirmed, that the Celtics have signed free agent center Jermaine O’Neal for two years at the full mid-level exception.

O’Neal’s addition shores up the center spot, which is in flux following Kendrick Perkins‘ knee surgery and the expected retirement of Rasheed Wallace. By using the full MLE, the Celtics now are shopping for players with the the veteran minimum contract and the allure of playing on a championship contender.

The length of O’Neal’s deal also completes the framework of the Celtics’ window of opportunity with their veteran group. O’Neal’s deal will expire at the same time as Kevin Garnett‘s and Ray Allen‘s. (Allen has a player option for the second year).

The only players signed beyond the next two seasons are Paul Pierce, Rajon Rondo and rookie Avery Bradley.

As noted earlier today, Ainge still has Wallace’s contract to dangle in trade talks, should Wallace follow through on his intention to retire. Ainge can also re-sign his own team’s own free agents, with Tony Allen figuring to be the next Celtics target.

Here’s the Celtics’ updated roster as of this afternoon:

PG: Rajon Rondo, Avery Bradley, Oliver Lafayette (non-guaranteed contract)

SG: Ray Allen

SF: Paul Pierce, Luke Harangody (second-round draft pick)

PF: Kevin Garnett, Glen Davis, Tony Gaffney (non-guaranteed)

C: Kendrick Perkins, Jermaine O’Neal, Semih Erden, Rasheed Wallace