Bielik started playing football for his hometown club, Górnik Konin before being spotted by Lech Poznań scouts in 2012, and later joining their developmental academy. He won the Polish U-17 Championships with the club in early 2014.[1] However, in July 2014, Bielik joined Lech's archrivals, Legia Warszawa for £8,800 (50,000 zł),[2][3] and on 24 August, made his Ekstraklasa debut against Korona Kielce.[4]
In early 2015, Arsenal had agreed a reported £2.7 million deal for Bielik with Legia Warsaw.[5] On January 21, Arsenal completed the Bielik deal with the Polish midfielder signing for an undisclosed fee, subject to regulatory processes.[6]
