The Pittsburgh Penguins placed defenseman Mike Matheson on injured reserve, retroactive to Friday, because of an undisclosed ailment.

Coach Mike Sullivan announced Matheson would be sidelined for an indefinite period of time following Sunday’s 4-3 shootout win at PPG Paints Arena.

“He was injured in the (Friday’s) game,” Sullivan said via video conference. “Right now, his status is longer term. I don’t have a time frame for you at this point.”

In his absence, the Penguins dressed defenseman Juuso Riikola. Making his season debut, Riikola logged 14 minutes, 31 seconds of ice time on 19 shifts.

In two games this season, Matheson has no points. The Penguins acquired the 24-year-old blueliner along with forward Colton Sceviour in a trade Sept. 24 that sent forward Patric Hornqvist to the Florida Panthers.

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