"I've got to get my ankle better," Gallen told Sky Sports Radio.
"I'm in a brace for a week or two with that, so the preparation for the fight might take a bit of a hit there.
"In two or three weeks I'll be right with the ankle and get into training."
Gallen's last fight saw him win by unanimous decision over mixed martial arts fighter Randall Rayment at the Footy Show Fight Night in Sydney on January 31.
He fought twice in 2014 and claimed two TKO's, beating Herman Ene Purcell in February, before dealing to former teammate Anthony Watts in one minute and 28 seconds last December.
Prior to that, Gallen began his boxing foray with two amateur bouts in The Fight for Life event in Auckland, scoring a knock-out against former All Blacks hooker Hika Elliot in 2012, and claiming a split decision against current All Blacks loose-forward Liam Messam.
The extent of Thompson's boxing background is unknown, but the former Gold Coast Titan donned the gloves for a charity bout in 2011.