Malan has compiled 694 runs at an average of 53.38 and could open the innings.
Andrew Puttick is in the squad, but will resume duties behind the stumps and could bat lower down as Vilas is at home to care for his wife and new-born son, James.
The imminent birth of the new-born of Rory Kleinveldt and his wife, Reyhana, has also ruled the fast bowler out of the domestic four-day clash.
Justin Ontong, the Cobras skipper, is also not available for the crucial encounter. He will be at the side of his wife, Lee-Anne, who is also set to become a mother in the next few days.
The Cobras made some enforced changes due to injury concerns to Mthokozisi Shezi (side strain) and Justin Kemp (swollen ankle).
Robin Peterson has taken over the mantle of captain in the absence of the long-serving Ontong.
Paul Adams, the Cobras coach, said their approach would be to be positive and to win as many matches as possible in the next six weeks.
An attacking mind-set and a positive brand of cricket is a prerequisite for success.
The Cobras boast several players who can win matches single-handedly. They include Peterson, Beuran Hendricks, Dane Piedt and the top-order stalwarts like Levi, Malan, Puttick and Van Zyl.
But the Cobras will rely heavily on especially Van Zyl to score heavily and secure at least a century, as a lack of first-innings runs has hampered their progress this season.
The Cobras squad is: Robin Peterson (capt), Stiaan van Zyl, Andrew Puttick, Richard Levi, Pieter Malan, Omphile Ramela, SA Engelbrecht, Lesiba Ngoepe, Dane Piedt, Beuran Hendricks, Dane Paterson, Travis Miller, Lizaad Williams.