Born in Bilbao, Biscay, Basque Country, Undabarrena made his senior debut with local side Santutxu FC in 2012, in Tercera División.

In 2014, after a year at JD Somorrostro in the regional leagues,[1] he moved straight to Segunda División B with SD Amorebieta.

[2] He agreed to a deal with fellow league team CD Mirandés on 8 January 2018,[3] but moved to Burgos CF in the same category on 20 July, on a two-year contract.

[4] Undabarrena became a regular starter for the Burgaleses, and helped in their promotion to Segunda División in 2021 as team captain with two goals in 25 appearances (play-offs included).

[5] He made his professional debut at the age of 28 on 15 August of that year, starting in a 0–1 away draw against Sporting de Gijón.