He had already been booked and it wasn't reckless and I don't think that it was deliberate but it was quite late, the ball was already gone and he could have, or should have, been booked again, which would mean a red card," Bilic said.
The coach added in his news conference: "I saw that incident again, I don't think it was reckless. It was from my point of view not deliberate, but it was very late.
"Nine times out of 10 you see that challenge and get one [a yellow card] -- unfortunately this was the 10th time."
Chelsea manager Antonio Conte disagreed, saying in his news conference that Costa pulled out of the challenge before colliding with Adrian.
"I must be honest -- Diego tried to put pressure on Adrian and then before he had the contact he stopped it," Conte said. "For this reason I think the referee took the right decision.
"We know Diego is a passionate man and he puts passion in everything he does. But in this situation I think the referee took the right decision.