"It was a big setback for us to lose Malcolm so early in the match," Lions coach Swys de Bruin told South African media.
"He will definitely fly back on Monday and will do his scans in Joburg."
If he is sidelined for a lengthy period, Marx's influence will be just as sorely missed by South Africa when England tour the republic in June.
Always a dynamic ball carrier, Marx has added an accurate lineout throw to his repertoire in the last couple of seasons - a key factor for a Springboks side which has always relied on solid set piece possession.
Stormers hooker Bongi Mbonambi was Marx's understudy for most matches last year but was ruled out for at least three months in March after suffering a burst appendix in February.
South Africa face Wales in Washington DC on June 2 before tests three test against the English tourists in Johannesburg, Bloemfontein and Cape Town on the following three Saturdays.
(Reporting by Nick Mulvenney; Editing by Sudipto Ganguly)
