Surrey captain Graeme Smith could miss the rest of the season after suffering a fractured knee.
The South African has been playing through the pain in recent days, but has flown home for surgery on the problem.
Surrey moved swiftly to find a replacement and have signed Hashim Amla for a month, with the batsman expected to feature at the weekend in the County Championship clash against Essex.
Smith has been plagued by fitness problems during his spell at Surrey as his first season was cut short by ankle surgery.
Director of Cricket Alec Stewart has welcomed the arrival of Amla, a former international team-mate of Smith, but is sad to lose the experienced batsman.
"Whilst it is obviously a huge blow for Graeme to be heading home, especially after his recent match winning hundred, and with the impact he was having in the dressing room, we are very fortunate to be able to welcome back Hashim Amla for the next month," said Stewart.
The captaincy has been handed to Gary Wilson, who said: "It's a huge honour and a privilege to be asked to captain Surrey. I can guarantee everyone I'll be doing my best to fill the huge shoes left by Graeme's unfortunate injury."