The North Queensland club says a cousin of Robert Lui is to blame for a controversial comment sent out on the halfback's Twitter account.
The NRL sought an explanation after the tweet appeared while Johnathan Thurston lined up a second half penalty goal for North Queensland in their win over Canberra in Townsville on Saturday, a match Lui missed due to injury and watched from the bench.
"Don't go for 2. I need 13+,'' the tweet read, in apparent reference to a margin bet.
NRL players are banned from betting on matches and face sanctions if they do.
The Cowboys issued a statement on Monday saying the tweet was "inadvertently'' sent from Lui's account by an unnamed cousin.