Panathinaikos attempted to make a run at the three NBA big men over the course of the last two weeks before eventually deciding instead to sign Armstrong.
The news was announced today by the club in a press release.
While the 6-foot-11 forward and center has not played in the league since last playing 12 games for the Atlanta Hawks during the 2010-11 season, Armstrong possesses the size, length and skill level the Greek power house club was searching for.
Since taking his game overseas, Armstrong has played two seasons in France with ASVEL where he averaged 11.1 points and 7.2 rebounds last season during 29 French League games.
The 12th overall pick in the 2006 NBA Draft, Armstrong also appeared in the NBA with New Orleans, Sacramento, Houston and Washington before moving on briefly to play for the Hawks.