The Capitals will retain 31% of Eller's $3.5 million salary cap hit.
Eller, 33, has been a consistent veteran presence for the Capitals since he was traded to Washington from Montreal before the 2016-17 season. A tough, two-way center with good defensive instincts, Eller projects to slide into the Avalanche's bottom-six rotation and can contribute on the penalty kill.
He also brings championship pedigree to the reigning Stanley Cup holders. Eller was part of the Capitals' run to a title in 2018, scoring seven goals and 18 points in 24 playoff games. The Avalanche received important contributions last spring from deadline acquisitions slotting onto their third and fourth lines -- most notably Artturi Lehkonen -- and Eller could fill a similar role in Colorado's quest for back-to-back Cups.
This latest trade by Washington fits the bill on what general manager Brian MacLellan has been focused on ahead of Friday's 3 p.m. ET deadline. Eller is a pending unrestricted free agent this summer that the team either couldn't, or didn't intend to, re-sign. MacLellan has moved several experienced players over the past week, including Dmitry Orlov, Garnet Hathaway, Erik Gustafsson and Marcus Johansson.
At the same time, MacLellan has acquired high draft choices and a young roster player (22-year-old defenseman Rasmus Sandin) to start stocking up Washington for the future. The Capitals also signed defenseman Nick Jensen -- an irreplaceable member of the blue line -- to a three-year, $12.15 million extension Tuesday.
Washington is on the outside of the playoff picture, sitting five points back of the second Eastern Conference wild-card slot.