De Wit, who joined from the Lions, was seen as a solution to the Stormers problems in the openside flank role.
The Stormers confirmed the injury after De Wit broke the news via Twitter. However, there was no word on a how long he will be out for.
De Wit is one of five new recruits at the Cape franchise. The other four are Sarel Marais, hooker Ramone Samuels, loose forward Johan du Toit and utility back Dan Kriel.
Hooker Siyabonga Ntubeni (Achilles)and wing Leolin Zas (leg) are the other two players in the 50-man wider training group that are currently sidelined with significant injuries.
Meanwhile, centre Huw Jones could be leaving the Stormers at the end of Super Rugby.
Last year, it was reported that the Scottish Rugby Union have enquired about bringing Jones to either Edinburgh or the Glasgow Warriors.
There is a rumour doing the rounds that Jones could be joining the Warriors. However, there was no confirmation on Jones' long-term future from the Stormers.
"He [Jones] is contracted to us for the rest of the season, just like Cheslin [Kolbe]," a Stormers spokesperson told rugby365.
Kolbe will be joining French giants Toulouse at the end of this year's Super Rugby tournament.
Stormers wider training group: Juarno Augustus, Nizaam Carr, Jaco Coetzee, Kurt Coleman, Damian de Allende, Juan de Jongh, Jan de Klerk, Pieter-Steph du Toit, Daniel du Plessis, Jean-Luc du Plessis, Robert du Preez, Dewaldt Duvenage, Rynhardt Elstadt, Eben Etzebeth, Martin Ferreira, Huw Jones, Oliver Kebble, Eduan Keyter, Cheslin Kolbe, Siyamthanda Kolisi, Dan Kriel, Dillyn Leyds, Wilco Louw, Frans Malherbe, Godlen Masimla, Sarel Marais, Mbongeni Mbonambi, Khanyo Ngcukana, Sikhumbuzo Notshe, Caylib Oosthuizen, Justin Phillips, Ramone Samuels, JD Schickerling, Seabelo Senatla, Chad Solomon, Brandon Thomson, Kobus van Dyk, JC Janse van Rensberg, Jurie van Vuuren, Frans van Wyk, Chris Van Zyl, Ali Vermaak, Jano Vermaak, EW Viljoen, Cobus Wiese, Damian Willemse, Eduard Zandberg.
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