England captain Owen Farrell has tested positive for Covid-19 on the eve of Saturday's Autumn Nations Series opener against Tonga.
Farrell will miss training on Friday but the Rugby Football Union (RFU) said he may still be able to play the match.
The 30-year-old is isolating and will take further tests on Friday.
On Thursday a member of England support staff tested positive but the RFU says "England are continuing preparations" for Saturday's match at Twickenham.
A statement added that all other players and staff had received negative results after a further round of testing on Thursday.
Farrell is due to start at fly-half, with Marcus Smith on the bench after he missed several training sessions this week with a minor leg injury.
With George Ford left out of the autumn squad, Henry Slade - who is down to start at 13 - or replacement George Furbank may have to offer back-up at 10.
The RFU expects to know more about whether Farrell can play on Friday afternoon.
England: Steward; Radwan, Slade, Tuilagi, May; Farrell (capt), Youngs; Genge, George, Sinckler, Itoje, Hill, Lawes, Underhill, Curry.
Replacements: Blamire, Marler, Stuart, Ewels, Dombrandt, Mitchell, Smith, Furbank.
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