The stars previously teamed up on last year's (11) We Found Love, and the Umbrella hitmaker was reportedly keen to work with Harris again.
However, the producer admits he found it hard to write a suitable tune for the star's latest offering Unapologetic in enough time.
He tells Bbc's Newsbeat, "Rihanna's been recording her next album and I saw her and she said, 'You have to do something for my album, you have to, we need you' and then you're like, 'Right, I need to do this!'. You go into the studio and you're like ok, I need to sit here, I've got two days to make probably one of the best records that I will ever have made in my life, let's see how that works out.
"Obviously, I didn't do anything so I'm not on the record. I did a decent tune but you can't work under that kind of pressure, I can't anyway."