The Spaniard appeared to make minimal contact with Courtois before going down inside the box.
"Our start was maybe not the best. We lost too many balls," said Courtois.
"The red card was very light and the penalty was a clear dive. I tried to make myself small and if a striker puts his feet there.
"He clearly left his foot and dived, it shouldn't have been a penalty. In the second half we tried to fight with 10 men, we got a goal and instead of trying to look quickly for a second goal maybe we should have regrouped.
"We all know this kind of player. They see a goalkeeper coming, he manufactured the content. It was very, very light.
"I think we have to find our form from before new year. We have a tough month coming up. It is important for us to continue to work - heads high."