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Jason Roy had to miss England nets after suffering a back spasm and will have to prove his fitness by taking a full part in training on the eve of the first one-day international.
Roy sat out the remainder of England's practice session at the Mangaung Oval, two days before the start of their series against South Africa, after hurting his back in Monday's warm-up session.
England expect him to be able to bat on Tuesday, something he must do if he is to open the innings the next day.
Should Roy's back problem persist, England's most obvious contingencies are to either promote James Taylor up a position from number three - with Joe Root back to reclaim that spot - or push their World Cup opener Moeen Ali up the order again.
England's hosts have been left with much to ponder too after a raft of injuries to their pace attack - and their latest move is to call David Wiese into the squad for the first two matches, in Bloemfontein and Port Elizabeth.
Wiese, like Marchant de Lange who was added to the squad 24 hours earlier, had little joy against England for South Africa A in Kimberley on Saturday when he finished with figures of two for 73 in a 163-run defeat.
The 30-year-old, who played three ODI against New Zealand in August last year, joins De Lange in the squad after initial injuries for Dale Steyn and Kyle Abbott and then Albie Morkel's back spasm.
Veteran bowling all-rounder Morkel may yet be fit for the final three matches.
There is much uncertainty therefore about South Africa's pace resources, but all-rounder JP Duminy insists the hosts are still in good shape after winning their last two ODI series - including, most recently, in India.
"I don't think we're weakened. I think the replacements are good enough to stand in for those players," he said.
"It's not an interruption in any way for us. We know what's needed as a squad and it's important for us to stay unified as a team, no matter who the personnel are.
"The confidence from the one-day cricket point of view has been pretty good... we've won our last two series.
"But we know this is a tough challenge that faces us, and that England have also been playing really well in this format."
England's Adil Rashid, like his fellow spinner Duminy, may have a significant role to play in what is likely to be a high-scoring series.
Rashid will approach the challenge with confidence high after making such a success of his Big Bash secondment to Adelaide Strikers, instead of joining England for their Test series success here over the past two months.
The Yorkshire leg-spinner made it clear he never entertained the notion of taking in another Twenty20 stint at the Indian Premier League this spring - preferring instead to stay with the county champions in the early months of the English season and perhaps press for more Test caps after the three he earned against Pakistan in the United Arab Emirates before Christmas.
Rashid said of his Big Bash experience: "It went well personally for me.
"It was a chance to play against different players in different conditions in what is probably now one of the biggest competitions in cricket, after the IPL.
"It was a great experience to play in front of 40-50,000 people.
"It was a good decision to go out there, playing in a big competition as opposed to being here and maybe not getting any match practice."
His only trip to India this spring, though, is likely to be with England for the ICC World Twenty20.
Rashid added: "I don't have anything to do with the IPL as yet.
"I've had no discussion as yet - nothing whatsoever."
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