The 35-year-old, who will undergo an examination of the problem on Tuesday, was unable to complete his 11th over for Hampshire against Nottinghamshire at Southampton and was forced to leave the field.
Steyn has had a horrible run of injuries over the last two years, hampering his bid to become South Africa’s record test wicket-taker, though he did equal the record in Sri Lanka last month.
Steyn and Shaun Pollock have each taken 421 test wickets.
A serious shoulder injury kept him out for most of last year before a heel problem sustained in his comeback test against India in February sidelined him once more.
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(Reporting by Mark Gleeson in Cape Town; Editing by Peter Rutherford)
