Reilly was omitted from the Crows team to play Richmond a fortnight ago and used the extended break to work on his conditioning, which included more running and fewer weights sessions.
Adelaide assistant coach Scott Camporeale said he expected the 2012 All-Australian nominee to benefit from a break and a lighter frame.
"The game's getting quicker and faster and guys need to cover the ground a lot easier and we just thought that it'd be in his best interests that we needed him to just slim down a bit," Camporeale said.
"He did a fair bit of [endurance work], changed his weights program [over the break] and he's looking really good.
"It's just a little bit of muscle [lost] for him, you can see he's a pretty finely tuned athlete.
"Particularly where he's playing down back, we need a lot of run out of there."
Reilly hasn't had the opportunity to play himself back into form after a back injury ruled him out of the SANFL last weekend.
"What we've seen with Brent's training and his attitude has been a fair bit more upbeat," Camporeale said.
"Sometimes you just need a circuit breaker
"He's too good a player not to be playing AFL footy so we're going to back him in and give him another shot."
Reilly flew out with his teammates, including the recalled Aidan Riley and Brad Crouch, for the Gold Coast on Friday morning, ready to take on the Suns on Saturday.
Guy McKenna's team have the easiest run home of any side, playing four of the bottom six sides in their last 10 games.
Camporeale agreed the trip to Metricon Stadium was quickly becoming a tough road trip.
"[They're] certainly not the easy beats anymore, they're travelling really well and their good players are playing really well," he said.
"Their speed, their skill and they've got some really impressive talls that can mark it so it's going to be a tough game for us."
