Lightning right winger Ryan Callahan is out indefinitely after undergoing an emergency appendectomy Monday night, per multiple reports and a team source who spoke to ESPN.com's Pierre LeBrun.

The 30-year-old had abdominal pain late Monday afternoon before checking into Tampa General Hospital for surgery, the team source told LeBrun.

Team spokesman Bill Wickett said Callahan's return to the ice is "undetermined" at this time.