The 41-year-old Du Plessis injured his thumb while fielding against MI Cape Town on Saturday at the Wanderers and did not come out to bat in the run-chase.
Super Kings head coach Stephen Fleming said after the game: "He got his thump jammed in the ground which has done some damage.
"Obviously enough damage not to bat which was [not good], when you are chasing 200 you need your star players to be out there.
"So, to lose him is another factor but we'll take into consideration what happens going forward, we are hoping it's bruising and settles down but I don't think I feel overly optimistic with the amount of injuries we've had so far.
"A bit of a pessimistic view on these things, so I'm hoping for the best but we may have to prepare for other means."
Leus du Plooy has been added to the Super Kings' squad for the remainder of the campaign.
The Super Kings currently sit third in the standings after winning three of their seven encounters so far this season.
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