"Both went for further investigations and specialist opinions and it was decided to rather withdraw them from the Springbok squad for the series against England," a statement said.
No details of their injuries were given.
Both Du Plessis and Steyn played the full match as their Montpellier side were beaten 29-13 by Castres at the Stade de France on Saturday.
Du Plessis, 34, was set to make his first appearance for the Springboks since the 2015 World Cup, recalled to fill the void left by the injury to hooker Malcolm Marx.
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Steyn, 31, had also been expected to start at inside centre, although new South Africa coach Rassie Erasmus had previously said on Monday that neither would be considered for Saturday’s first test at Ellis Park in Johannesburg because they were late in joining the squad after the completion of the season in France.
(Reporting by Mark Gleeson in Cape Town; Editing by William Maclean)
