Selectors confirmed on Thursday night that Maddinson had been called into the Test squad, after not featuring in Australia's red-ball side for almost 10 years.
Sam Harper has also been drafted in as a back-up wicketkeeper, with a finger fracture now officially ruling Josh Inglis out of the first Test in Durban starting next Friday.
Inglis was hurt while playing in the series-opening ODI against South Africa last week, with further scans back home in Perth revealing a fracture.
There are now similar concerns around Green following the third ODI in Potchefstroom on Wednesday, after he hurt his abdomen trying to pull a ball while batting in Australia's dead-rubber win.
Australian medical staff will now keep close watch on the allrounder, who will be "assessed further" in the coming week.
Regardless, the latest abdominal injury will raise question marks over Green's ability to bowl, after having not done so yet in a game on this tour.
The one bit of good news for Australia is opener Matt Renshaw has been cleared of a wrist injury after being hurt while fielding in the final ODI.
But the injuries do leave Australia's line-up for the first Test largely up in the air, with up to two spots in the top-six unclear if Green is not fit.
Inglis had stood a chance to come into the side for Marnus Labuschagne, if selectors had opted to drop the Queenslander for the series opener.
Maddinson could now fill one of those roles, with Cooper Connolly the other reserve batter in the Test squad.
Maddinson last played a Test at Boxing Day in 2016, and has since overcome a battle with testicular cancer to restart his cricket career.
The 34-year-old did not play a first-class match last summer, but struck 126 for NSW in a one-day match against Victoria last week.
Harper looms as another option, after being called into his first Australian squad at age 29.
The Victorian was the second-leading run-scorer in last summer's Sheffield Shield with 677 at 35.63 and is fresh off hitting a century for Australia A against India A in Pudcherry.
"Sam give us wicketkeeping cover as Josh continues his recovery while Nic provides flexibility throughout the batting order," chief selector George Bailey said.
Australia will play an intra-squad warm-up match in Potchefstroom this weekend, before moving to Durban on Monday to commence preparations for the first of three Tests.
