Recent reports revealed that the actress will not appear in the next season while Paget Brewster will star in fewer episodes.
Writing on her Twitter page, Brewster dismissed claims that the decision had been taken for creative reasons.
"'Creative Reasons' has been an Executive Bulls**t excuse for decades," she said. "It is financial. AJ is a dreamboat. And yes, I am hurt too."
Meanwhile, Thomas Gibson posted: "To say we're all mystified and disappointed is an understatement. All the fan support is much appreciated! Stay tuned."
Elsewhere, Deadline reports that Criminal Minds star Kirsten Vangsness has signed a petition set up by fans urging producers to hire Cook again.