Career
He made his debut at the senior level in 2008. Mattila was the captain of the Finnish under-19 national team Early career
Before the season 2008, HJK was on a training camp in Marbella and Mattila was spotted by scouts of Sevilla Football Club and Málaga CF. He was playing on schoolboy terms, but HJK managed to sign a three-year contract with him.
In August 2008, Serie A club Palermo called him up for a week-long trial after scouting him in Helsinki.
Just a week after his visit to Palermo, Udinese Calcio called him up for a week-long trial. Before leaving to Udine, Mattila stated that he is ready for a move to Italy.
In October, Iltasanomat told that Udinese had made an offer, but HJK rejected the first bid. The asking price was said to be around 700.000 euros.
After rumours about his move to Udinese, Mattila stated that he wants to make a career in Italy and was hoping for a move in the next transfer window.
Udinese Calcio
In November 2008, he signed a 4.5-year contract with Udinese and joined the club in January 2009. He played with the Primavera team and in July 2009 left on loan for Ascoli. On 10 August 2010 he was loaned again.
This time to Air Corps Bellinzona, playing in the Swiss top level
On 29 July 2012, it was announced that Mattila had joined his former club, HJK, on loan until October 2013. Aalesunds FK
On 3 November 2013, it was announced that Mattila has signed a three-year contract with Aalesunds FK in Norway"s Tippeligaen.
Fulham Football Club
On 4 August 2015 Mattila signed for Fulham Football Club for an undisclosed fee.
