The 34-year-old has been plagued by back problems throughout his 15-year international career and his latest relapse is a major concern with a two-match Test series against West Indies six weeks away.
"Atapattu has been suffering from unbearable pain from a back injury and has been forced to seek medical treatment abroad," Sri Lanka Cricket's chief executive Duleep Mendis told reporters on Thursday.
Atapattu, who sustained his latest injury in a training session in Colombo, is expected to seek help in Australia and is due to leave Sri Lanka on Thursday night or Friday morning.
Officials hope he will be fit in time for the first Test against West Indies in Colombo which is tentatively scheduled to start on July 15.
