England are hopeful that captain Joe Root and Jos Buttler will bat in the second innings of the first Test in South Africa despite illness.
Root spent time off the field on day three in Centurion, while Buttler did not feature.
Batting coach Graham Thorpe said it would have been "a struggle" for Root or Buttler to bat on Saturday.
"They have been under the weather today - that's why it was even more important we got some runs," Thorpe said.
Speaking to the Test Match Special podcast, he added: "Hopefully they can get a decent night's sleep and be fitter than they were today."
England will resume on 121-1 as they attempt to pull off what would be their highest successful chase in Test cricket, with the hosts setting a target of 376 to win.
It would surpass the Ben Stokes-inspired victory in the third Test of the 2019 Ashes series, when they chased down 359 against Australia at Headingley.
'We believe we can win'
Root and Buttler are the latest England players to be struck down a bout of sickness that has blighted their tour.
Chris Woakes, Mark Wood and Jack Leach remained at the team hotel rather than travelling to the ground on Saturday, while Ollie Pope, Joe Denly, Jofra Archer and Stuart Broad have also been affected by flu-like symptoms on tour.
Stokes was treated for dehydration on the opening day of this match, while Jonny Bairstow kept wicket in Buttler's absence.
"We've got a lot of disinfectant cream in the dressing room and our doctor is giving us a lowdown on how to look after ourselves," Thorpe said.
"It's tough when you're in this environment. It is going to spread a little bit."
Victory is unlikely but England's extraordinary win at Headingley in August has given the team belief.
Sri Lanka chased down 304 against South Africa in Durban in February, and the hosts have lost their past five Tests.
Opener Rory Burns was disciplined on Saturday to make an unbeaten 77, while Joe Denly, who made 50 in the first innings, will resume in the morning on 10.
"We've got a chance. It's certainly not going to be easy but the belief in the camp is there," Thorpe said.
"We know the fight we've got in our dressing room and what we're going to try and achieve tomorrow."
Meanwhile, South Africa opener Aiden Markram has been ruled out of the four-Test series with a fractured finger on his left hand.
The 25-year-old, who suffered the injury on Friday, will have surgery early next week and will be sidelined for at least six weeks.
He made 20 in the first innings and two in the second at Supersport Park.
|England's highest successful Test run chases|
|362-9 v Australia, Headingley, 2019|
|332-7 v Australia, Melbourne, 1928|
|315-4 v Australia, Headingley, 2001|
|307-6 v New Zealand, Christchurch, 1997|
|298-4 v Australia, Melbourne, 1895|