He spent the 2006–07 season on loan at Boavista from Pogon Szczecin. In June 2007, he signed a three-year deal with the Portuguese club. He transferred to Greek side Skoda Xanthi in January 2008. On 30 June 2009, it was reported that Steaua București have signed the Polish midfielder from Skoda Xanthi.[1]
On 23 July 2009, he scored his first goal for Steaua București in a UEFA Europa League match against Újpest FC; he scored the second goal in the 2–1 victory. On 2 August 2009, Grzelak played his first Liga I match in Steaua's shirt against Ceahlăul Piatra Neamţ, Steaua won away with 2–0.
In January 2010, Grzelak was demoted to the B squad.
In August 2011, he joined Ruch Chorzów on a one-year contract.[2]