Maddocks departed the Rebels earlier this month to join the Waratahs, citing a personal desire to shift home.
Kellaway was disappointed to lose his former schoolmate without playing a game together, even if it could work in his favour.
“Jack’s a huge loss, he’s a very talented player,” Kellaway said on Tuesday.
“There’s lots of depth in the outside backs but it does make life a little easier for people like me trying to break in there.”
Standing in his way are current Test players Marika Koroibete, Dane Haylett-Petty and Reece Hodge while Billy Meakes, Tom English and Campbell Magnay are among the other contenders for starting positions.
A stand-out of the Wallabies’ World Cup campaign, Koroibete in particular has impressed Kellaway.
“He’s a freak,” Kellaway said.
“He’s very fast, very strong, he gets on with his work and doesn’t say much.
“He’s awesome – a great guy to play with and a great guy to hang around and he’s teaching me some Fijian which is pretty nice.”
Kellaway has also been soaking up the knowledge of Rebels skipper Haylett-Petty, whose career followed a similar path with an early stint in Super Rugby and then a stint overseas before returning to Australia.
“He’s a quality player for me to be able to sit there and pick his brain and watch what he does, probably more off the field than anything, that’s pretty cool,” Kellaway said.
Spending the past 12 months playing in the UK with Northampton and Counties Manukau in New Zealand, Kellaway returned to Australia with the ultimate goal of a Wallabies berth.
The 24-year-old, who had 25 Super Rugby matches with the Waratahs between 2015 and 2018, hoped his versatility would be an advantage as well as his oversea experience.
“I can fit into multiple spots and that’s a valuable asset for the team,” he said.
“It’s not something you want to do all the time but if it’s beneficial for the team than that’s the way it’s got to be.
“I feel like I’m in the best place I’ve been for a while with my rugby and I probably wouldn’t be there if not for my experiences.”