Gallen's suspicions about ASADA date back to the 2011 supplements scandal which hit the Sharks.
"I think it's pretty clear that I'm not a fan of ASADA," he told 2GB's Wide World of Sports Radio.
"That's all been dealt with now, but certain things I saw which I've written in my book about, now after seeing this as well, you have to think whether ASADA are trying to create headlines.
"Are they really there for the good of the game? Are they really trying to catch people doing the wrong thing or are they just there to create headlines."
Gallen said the authorities could be seen as legally culpable if an "enhanced" player who had tested positive was still able to play through such a long delay and then injured an opponent.
Former ASADA boss Richard Ings claimed the delay "isn't a crazy deadline".
"It is a complicated sample with a wide variety of banned substances detected and needing confirmation at a time when Christmas, fires and then COVID were impacting," he said.
Gallen said: "At no point here am I trying to justify what's happened. If Bronson has tested positive then he'll cop whatever punishment that is coming his way, but surely there's got to be some questions asked of the timing of this."
Xerri is alleged to have returned a positive A-sample "for exogenous Testosterone, Androsterone, Etiocholanolone and 5b-androstane-3a,17b-diol" when tested on November 25. He was recovering from shoulder surgery at the time, and he missed the first two matches this year.