Mathews left the field early on in Scotland's innings in the match at Hobart, and was not seen again until the presentation. Vice-captain Lahiru Thirimanne said Mathews had not gone for a scan on Wednesday night, but suggested he may do so on Thursday. Mathews had felt the pain during his innings of 51. He did not bowl, for the first time in the tournament.
"He's strapped up at the moment, but hopefully he'll be okay," Thirimanne said after the match.
The stitches on Herath's spinning finger are due to be removed on Thursday, and he is expected to resume bowling in the nets on Friday. Sri Lanka have flown in offspinner Tharindu Kaushal as cover for Herath, but a replacement is unlikely to be necessary, Thirimanne said.
"I think he has about an 80% chance of playing in the quarter final. I feel he will be fit," Thirimanne said.
Mathews is the sixth Sri Lanka player to fall under an injury cloud in the tournament. Seamer Dhammika Prasad, legspinning allrounder Jeevan Mendis and batsmen Dimuth Karunaratne and Dinesh Chandimal have all had to be replaced, after sustaining World Cup-ending injuries, while Herath is the other man to miss matches thanks to the cut on his finger.
"We have been in Australia and New Zealand for three months now," Thirimanne said. "We have to manage our bowlers very carefully, because it's a very long tour. We have hopefully another three matches left. So we need to have the best combination, and we need to manage our bowlers carefully at training over the next five to six days."