Uruguay striker Luis Suarez remained a great World Cup unknown on Tuesday, nursing his fragile left knee during a light workout just four days before his team faces Costa Rica in their Group D opener.

The Liverpool star had keyhole surgery on his left knee on May 22, and it is unclear how much he will play at the World Cup.

Suarez trained separately from his teammates, taking soft shots and making easy passes with his right leg — seldom using the left — as three members of the training staff looked on. As his teammates played a training match, Suarez trotted on the sidelines.

Suarez may be rested for the first match, saving him for the more difficult games against England and Italy.