The Wales defender, released by West Ham last month, played in last night's 13-0 friendly win away to Cornish amateurs Tavistock.
Gabbidon made just 92 appearances in an injury-hit six-year spell with the Hammers.
Warnock said: "We're just looking at Danny. I spoke to him last week and I told him to come to Cornwall - there's no pressure down there. He can come and train and we had a tough session yesterday morning."
Another of the trialists, Danny Webber, scored in the rout.