The Dallas Cowboys are expected to soon have another assistant coaching opening, but this time it will be a major loss on the defensive staff.

Cowboys linebackers coach/passing game coordinator Matt Eberflus will leave Dallas, a source said, to become the defensive coordinator under New England Patriots offensive coordinator Josh McDaniels once McDaniels lands a head coaching position.

McDaniels is expected to be named the Indianapolis Colts' head coach once the Patriots' season comes to an end, the NFL.com reported Monday. Reports also have McDaniels linked to the Tennessee head coaching job that came open Monday once the Titans parted ways with Mike Mularkey.

Wherever McDaniels lands, however, Eberflus will come with him as defensive coordinator.

Eberflus, 47, is well-respected across the league and was considered a top candidate to replace Cowboys defensive coordinator Rod Marinelli once he retired. Marinelli, 68, said late last season, however, he planned to coach again in 2018.

The 49ers reportedly had interest in hiring Eberflus as their defensive coordinator last offseason before they went with Robert Saleh in the role. Eberflus had an expiring contract with the Cowboys after the 2017 season.

Eberflus, who is from Toledo, Ohio, just completed his seventh season with the Cowboys. He followed Rob Ryan to Dallas from Cleveland when Ryan was hired as the defensive coordinator for the Cowboys in 2011.

Eberflus added the title of passing game coordinator in 2016. He's coached nine seasons in the NFL. He spent two years in Cleveland as the Browns' linebackers coach. He was last a defensive coordinator in the college ranks for Missouri from 2001 to 2008.

Eberflus excelled with the Cowboys, helping in the development of linebackers Sean Lee, Anthony Hitchens and -- this year -- Jaylon Smith. Eberflus also got the most out of linebacker Rolando McClain during his time in Dallas. Eberflus helped DeMarcus Ware and Anthony Spencer both earn Pro Bowl trips in 2012.