Gravalos competed for the men's 4 × 400 m relay at the 2008 Summer Olympics in Beijing, along with his teammates Stylianos Dimotsios, Konstadinos Anastasiou, and Pantelis Melachroinoudis. He ran on the second leg of the second heat, with an individual-split time of 45.66 seconds. The team finished the relay in fifteenth place for a seasonal best time of 3:04.30, failing to advance into the final.