England batsman Alex Hales could miss the third Test against South Africa in Johannesburg because of a throat infection.
The tourists, who lead 1-0 in the series, will decide on the opener's fitness on Thursday before the toss.
Many of Hales' team-mates have suffered from stomach bugs.
Hales, 27, who scored his maiden half-century in the drawn second Test at Cape Town, trained alone in the nets on Wednesday morning before returning to his hotel room to rest.
If he fails to recover, England are likely to promote Compton to the top of the order and bring in Gary Ballance at number three, reportedly.