Pittsburgh's blue line health continues to be a concern as yet another top-four defenseman heads to IR

The Pittsburgh Penguins have lost yet another top-four defenseman to injury.

On Tuesday, top defenseman Kris Letang was placed on injured reserve with a lower-body injury. He missed Sunday's game against the New York Islanders and joins fellow top-four defenseman Owen Pickering on IR.

Even though another top-four defenseman, Marcus Pettersson, was activated from IR ahead of Tuesday's game against Detroit, the Penguins have had three of their top-four defensemen go down in the month of December alone. 

As it stands now, Letang's injury is still classified as day-to-day. Pickering skated in a full capacity with the team on Tuesday morning.