Eranga was rushed to hospital as his team-mates took to the field for the second innings of the match and remains in Ireland where he is undergoing tests to determine the cause of his elevated heartbeat, which is understood to have reached an alarming 220 beats per minute.
The 29-year-old had gone out to bat in the first innings and faced a single delivery, the final ball of Sri Lanka's innings. According to the team management there were no warning signs of any ill-health and and they are not aware of Eranga having any previous heart conditions.
It was during Sri Lanka's warm-up in the innings break that Eranga realised something was wrong.
"At the time he called me and said 'something has happened to me'," said Matthews. "He was warming up and just before we went on the field, he said something happened to me, can you touch my heart because it is beating fast. I felt something unusual so I quickly called the physio and the physio went for the doctor with him. It was a shocking incident."
While Eranga's health is of the utmost concern, he received a separate blow on Sunday when the ICC deemed his action to be illegal. The seamer had been reported after the second Test against England in Durham and subsequent tests in Loughborough showed the flexion of his elbow exceeded the legal maximum of 15 percent.
ESPNcricinfo understands Eranga was not showing signs of undue stress before the ODI on Saturday and that doctors have ruled out anxiety as a cause of his condition.
"It has been a tough 48 hours for him," said Matthews, "And the whole team is behind him and we are fully supportive of him. It was an unfortunate incident just before we went on to the field."
"It's another unfortunate incident where his action has proved to be illegal and he will have to go back and work with the fast-bowling coaches and come back strong."
"We are very confident he will come through both - his condition as well as his action - so we are very supportive of him and the whole team are behind him."
Eranga will remain in Ireland until the results of the tests are known and, once he is declared medically fit to fly, he will then return to Sri Lanka.
His absence leaves a hole in a bowling attack that has already been depleted by injuries to Dushmantha Chameera and Dhammika Prasad, Sri Lanka are preparing to call in at least one replacement from the Sri Lanka A squad, which arrives in England tomorrow ahead of two four-day games against Pakistan, followed by a 50-over tri-series also involving the England Lions.
During the three-Test series Sri Lanka struggled with the early season English conditions but showed gradual improvements and Matthews hopes the change in formats will lead to a change in fortune for his side.
"It was pretty unfortunate that we haven't performed well in the Test series but we kept improving game by game and as time went on we really started hitting our straps and we had some convincing wins in Ireland," he said.
"But England is a completely different team, we still have to play our best cricket to beat them here."
"We haven't done well in the recent past but we've played a lot of T20 games rather than one-dayers. We are a forceful unit when it comes to one-dayers, we've got a good set of guys and a bit of experience."