The 23-year-old Kenyan international striker had been linked with a move to a number of French and Belgian sides this season, but settled for the Spanish side.
Olunga who asked to be left out of the international friendly against Mozambique is looking for more playing time after failing to break into the starting 11.
Moments after completing his move, Olunga promised to repay everyone who has been standing by him throughout his career by making them smile once he steps into the pitch.
Thanks be to God for making me realise this moment in my career. I trusted in you and you have once again make me see your goodness. All Glory is to you.
Thank you to everyone who has been there for me during good and bad times.,all i can repay you is by making you smile once i step in the pitch.
To my family,I salute you,without you all wasnt possible.
A new leaflet to write a historical story.
He posted on his Facebook page.