Despite no obvious incident having occurred to Smith, the former South Africa captain will return home for further treatment on a fractured knee, with Surrey officials quickly making the move to bring his old teammate to The Oval.
"You have to accept it, and the good thing is we've been able to get Hashim Amla over at short notice. Cricket South Africa have been excellent with their dealings and we'll have him for the majority of June and then we'll see where we are after that," Surrey's director of cricket, Alec Stewart, told BBC London 94.9.
"Hash knows the club, he thoroughly enjoyed being here last year. Hopefully he will score runs in the four to five four-day games he's available for, as well as the four Twenty20 games."
Amla, who played six County Championship games for Surrey last season, will be available for the game against Essex starting on Sunday.