On May 23, 2009, Calathes announced that he would bypass the NBA to play in the Greek Basket League. He agreed to terms with the elite EuroLeague club Panathinaikos Athens. The three-year deal paid Calathes around €2.4 million net income, in addition to providing him with a home, car, and endorsements, making for a total package commensurate with what the NBA rookie salary scale provided an early lottery selection. Despite his commitment to play in Greece, he was still selected in the second round of the 2009 NBA draft by the Minnesota Timberwolves. He was then traded to the Dallas Mavericks for a 2010 second-round draft pick and cash.