Mallett, a former Springboks coach, has been forced to name an inexperienced line-up after arriving in South Africa without 13 first-team regulars.
Front-row forward Michele Rizzo, who has just one cap to his name, is also set to start against the world champions in what promises to be a baptism of fire for many of Mallett's young players.
"It's not ideal for a young Italian development side to play the world champions," Mallett told reporters.
"But the challenge is to make sure that whatever happens, however many tries get scored, that the team puts that try behind them and play as hard as they can for the next 10 minutes.
"If we have enough players who do that I'll be proud."
The selection of McLean is of particular interest as he fills in at the problematic fly-half position.
The 20-year-old has appeared at under-age level for Australia and Mallett believes he has the potential to hold down the fly-half role in years to come.
"If he was in South Africa we might say it was too early to throw him in, but I would like to see what he can do and this is a good opportunity," he said.
"If he can show me things, particularly on defence, then I will be pleased. I would like to see if he can remain unflustered under the severe pressure he is likely to come under from the Boks.
"He has a lot of potential. For a fly-half he is certainly physical enough at 93 kilograms, and he has an excellent left boot."
Italy will conclude their brief southern hemisphere tour with a Test match against Argentina in Cordoba next weekend.
Italy team: Andrea Marcato, Kaine Robertson, Andrea Masi, Gonzalo Garcia, Matteo Pratichehetti; Luke McLean, Simon Picone, Josh Sole, Robert Barbieri, Alessandro Zanni, Carlo Antonio del Fava, Santiago Dellape, Carlos Nieto, Leornardo Ghiraldini, Michele Rizzo.
Replacements: Fabio Ongaro, Ignacio Rouyet, Jaco Eramus, Tommaso Reato, Pablo Canavosio, Enrico Patrizio, Riccardo Pavan.