Career
Kamenár made his first football steps in his hometown club Spartak Trnava. He went through all the youth squads, until reaching the senior team, where he made five appearances. He qualified with Artmedia to the 2005-2006 Union of European Football Associations Champions League group stage but he did not get a chance.
He became a first goalkeeper in the second half of the 2005-2006 season when Juraj Čobej had to undergo treatment for a brain tumor.
On 2 July 2009, the 22-year-old Kamenár left Artmedia Petržalka to sign a five-year contract for French side Football Club Nantes. He played 35 matches in his first season and finished 15th with Nantes.
In the next season he lost his position in the club and moved on a half-year loan to Sivasspor. There he made only one appearance against Manisaspor.
In June 2011, he signed for Sparta Praha on loan.
He played 11 matches for the Sparta reserve squad. On 21 January 2012, he signed a half-year loan with option for his hometown club Spartak Trnava. Kamenar completed a season-long loan move to Scottish giants Celtic Football Club on 31 August 2012 with the option to make the move permanent, but he eventually joined Hungarian side Győri European Theatre of Operations until 2016.