Diamantakos began his pro career in Greece in 2012, when he played in the Greek League with Panathinaikos, in a game against Peristeri.

[6] In summer 2018, Diamantakos followed the team's relocation to the island of Lemnos, under the name Ifaistos Limnou.

During the 2020-2021 season with Apollon Patras, Diamantakos averaged a career-high of 12.3 points, 8.2 rebounds, and 1.4 blocks per contest, in 16 games total.

During the 2021-22 campaign, in 16 games, he averaged 5 points, 2.9 rebounds and 0.4 blocks, playing around 12 minutes per contest.

In August 2022, Diamantakos signed with ambitious 3rd division club AO Mykonou, in a rather surprising move.