Mathews' absence could jolt the prospects of the islanders, who rely on him to bring balance to the playing XI - he often delivers 10 overs in One-Day Internationals (ODI) in addition to batting at No. 5. South Africa on Saturday at the Kennington Oval.
It was a similar struggle for the Sri Lanka bowlers as Guptill and Tom Latham (44) began the reply.
South Africa, on the other hand, has had a mixed year and recently, they lost the ODI series against England by 2-1.More news: German Ambassador: 'No, No, No' Feud Between Trump, Merkel
"But we're still humble at the same time and know that we have to work hard and take it one step at a time to win this", he added.
Black Caps captain Kane Williamson plays a shot against Sri Lanka on Wednesday.
Sri Lanka head into the Champions Trophy on the back of losses to Australia and New Zealand in warm-up matches. As many as nine bowlers were used by New Zealand but on a ground with small boundaries, Sri Lanka had no problem scoring briskly.
"Mathews. had complained of stiffness and pain, prompting the team management to conduct radiographic investigations which revealed a strain on the muscle", Sri Lanka Cricket said in a statement.More news: 'Refreshing and strange': Trump's demands drive wedge into North Atlantic Treaty Organisation
"The only slight concern I have for India is that its selection was perhaps a little conservative, but it is still very strong", he said.
South Africa: AB de Villiers (capt.), Andile Phehlukwayo, Chris Morris, David Miller, Dwaine Pretorius, Faf du Plessis, Farhaan Behardien, Hashim Amla, Imran Tahir, JP Duminy, Kagiso Rabada, Keshav Maharaj, Morne Morkel, Quinton de Kock (wk) and Wayne Parnell.
He had been declared fit for the 50-over showpiece event after a week-long high intensity training camp in central Sri Lanka.More news: Trump tweets against Germany
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