The 30-year old Brazilian is out of contract at the end of the season and the Reds are desperate to retain his services with news that Gold Coast United are determined to lure him away from Adelaide.
With Adelaide currently funded by Football Federation Australia, Cassio is highly likely to earn much more away from Hindmarsh Stadium although a Reds spokesman says they are supremely confident of keeping him at the club.
"Adelaide has signalled that it is interested in securing Cassio," the spokesperson said. "At this stage it looks positive."
Cassio joined the Reds from Santa Cruz in 2007 and has racked up 60 appearances during his time at the club.