The 36-year-old Jamaican suffered a strained left hamstring chasing a ball before lunch and, after slumping to ground, was assisted off the field by physiotherapist Denis Waight and squad member Mervyn Dillon and then carried into the dressingroom on a stretcher.
According to Waight, the extent of the injury was not immediately known, but although it did not appear as bad as first thought, it is unlikely Walsh would recover enough to bowl in a few days time.
The injury, which occurred with South Africa on 49 without loss in the 18th over, robbed the West Indies of its most consistent bowler in the series and his absence would certainly weaken an attack which is already cause for concern.
The West Indies are also worried about Curtly Ambrose - at 35, another veteran who is also suffering.
Ambrose has been suffering for some time from an injured left knee, and according to Waight, it is getting worse each day.