The 30-year old is out of contract at the end of the season but the Reds are determined to retain his services, especially after the form he has been in so far this season.
“We want to keep him (Cassio) and he's happy here," Coolen told the Adelaide Advertiser.
"He prefers to stay here and we have to find out how we can do this, of course.
"We spoke with him weeks ago about the (contract) situation but we'll see now what happens in a couple of days or weeks.
“He was one of the best players."