The former Alaves winger had his presentation on Monday.
Rioja said: "It is a very special moment and an important leap in my career. I am coming to a big club, a great club in Spain. It has taken a little longer than expected to get here, but the important thing was to be here. I had a clear idea from the beginning: I wanted to play for Valencia CF and I am happy and proud, as well as looking forward to playing here at Mestalla.
"It's a great opportunity. It's a big club, a historic club in LALIGA and it is a great opportunity to continue growing and improving. It is going to be an important challenge.
"The atmosphere has been very good in my first few days here. We have not had many days to train, as it was just a case of arriving and playing, but I quickly got the message. I know what he wants, we have a similar idea of football and he was important when it came to me being here."