Coach Lindy Ruff said after practice Monday that the operation was performed earlier in the day to relieve a buildup of fluid. Ruff said Niedermayer had been attempting to play through the injury since first feeling discomfort during the preseason.
Signed as a free agent this summer, the 17-year NHL veteran had only missed one game this season following the birth of his daughter in October. The checking-line forward has no goals and six assists in 21 games this year.
"I think you've got to give him credit for trying to get through it. But he just feels it was hurting his play," Ruff said. "So the best thing to do was to have it cleaned up."
Goalie Ryan Miller returned to practice after missing one game with a mild groin injury, which began to bother him in the third period of a 4-2 win over Los Angeles on Friday. Miller said he felt better after two days of rest, but added he'll see how he feels after another day of practice before determining whether he can play Wednesday.
Miller had gone 3-1 in four starts since returning after missing six games with a hip injury.
Forward Drew Stafford resumed practicing, but has not yet been cleared for contact after missing eight games with an upper body injury. Stafford won't play against Pittsburgh, but could return as early as Friday, when the Sabres host Toronto.
To replace Niedermayer and potentially Connolly, the Sabres recalled forwards Luke Adam and Colin Stuart from AHL Portland. Adam had no points in two games with the Sabres earlier this season. Stuart, a minor-league journeyman, signed with Buffalo in August, and played 51 games with the Atlanta Thrashers from 2007-09.