Eller was placed on injured reserve Friday, retroactive to Dec. 17, due to an illness, Tom Gulitti of NHL.com reports.
Eller notched an assist in Tuesday's 3-2 loss to the Blackhawks.
Eller logged an assist and three shots on goal in Monday's 6-2 win over Utah.
Eller is practicing with the Capitals on Thursday and is expected to play Friday in Colorado, as reports.
Eller won't be an option against the Maple Leafs on Wednesday, Sammi Silber of The Hockey News reports.
Eller was traded from the Penguins to the Capitals on Tuesday in exchange for 2027 third-round pick and a 2025 fifth-round pick.
Eller contributed an assist, one shot, one block and three hits in Saturday's 3-1 win over Montreal.
Eller notched an assist and two hits in Friday's 4-1 loss to the Hurricanes.
Eller recorded two goals (on three shots) and added two assists in Friday's 7-3 preseason win over the Blue Jackets.
Eller was one of six Penguins to play in all 82 games this season, registering 15 goals and 16 helpers.