The Spaniard felt aggrieved after referee Chris Foy awarded the hosts a spot-kick in the 32nd minute when former West Brom man Shane Long appeared to trail his leg in a coming together with Craig Dawson.
Ben Foster saved Nikica Jelavic's resulting effort, only for Liam Rosenior to head home the rebound to put Hull in front.
"We played well for the first 25 minutes but the penalty changed the game," he said.
"I don't know if it was or wasn't a penalty, but I have one question, why we did not get a penalty from a similar incident involving James Morrison in the second half?
"I think it was a bad decision from the referee.
"In the second half, it's the same situation (as the Long incident) in the other box and the referee doesn't whistle.
"Shane Long is a good professional, a good striker. I think he only wants the best for his team, it's normal."
