Born in Esztergom, Hungary, Hajnal started playing football at the local Zoltek SE in his hometown Nyergesújfalu.

He found it hard to make the breakthrough with the Royal Blues, and after a mere seven Bundesliga appearances he moved to Belgium in 2004.

[1] His performance in Dortmund's 4–0 win against Frankfurt on 15 November 2008—scoring once and assists for three goals—earned him a place in the Bundesliga Team of the Week and made Hajnal Man of The Match.

[4] Hajnal extended his contract with VfB Stuttgart on 7 January 2013 until June 2014 with an option for a further year.

Current manager of Ferencváros, Thomas Doll had been interested in signing Hajnal previously.

[8] However, Hajnal was unaware that Ferencváros intended to sign him a couple of weeks before the offer was made.

[10] On 7 March 2015, Hajnal scored his first goal in the 57th minute in the 2014–15 season of the Hungarian League against Győr at the Groupama Arena in Budapest.

Hungary finished a disappointing sixth in their qualifying group for UEFA Euro 2008 and have been out of the running for a place in Austria and Switzerland next year since the beginning of the qualification period.

The competition from Greece, Norway and Turkey was simply too strong for Hajnal and his team mates, who nevertheless beat Bosnia-Herzegovina home and away during the campaign.

During the management of Sándor Egervári (2010–present), Hajnal played his first match in the Wembley Stadium against England.