Pollard will fly to Argentina as cover while Porecki, who started all three tests against England in July, goes through the 12-day protocol obligatory for players who sustain serious head knocks.
Porecki's absence means a likely start for Folau Fainga'a (27) in the Wallabies' opening Rugby Championship test against the Pumas in Mendoza on Saturday, August 6th, with Lachlan Lonergan (22) backing up from the bench.
Pollard enjoyed a breakout season with the ACT Brumbies in Super Rugby this year and played seven matches despite being behind three Wallabies hookers in the pecking order at the Canberra-based side.
A target of National Rugby League (NRL) clubs before choosing to commit to the 15-man version of the game, Pollard started two matches for the Australia A team in the Pacific Nations Cup last month.
Australia coach Dave Rennie (58), who has had to deal with a lengthy injury list this season, will name his team for Saturday's test later on Thursday, August 4th.