Pakistan vice-captain and opener Salman Butt was taken to hospital after complaining of severe stomach pain after the opening day of the first Test against South Africa.
Team manager Talat Ali said Butt was still under observation and had undergone various tests.
"He came to me late at night and complained of severe stomach pain and we rushed him to the hospital," Ali told Reuters early on Tuesday.
"We don't know when the doctors will release him."
Butt fielded on the opening day but was replaced by Yasir Hameed on Tuesday. South Africa were 294 for three at the close of Monday's action.
Ali said clarification would be sought from the match referee as to whether Butt could open the innings when he came back on field.
