Rex Ryan says Mike McCarthy is going into a great situation in Dallas, but he doesn't believe McCarthy is the long-term solution at head coach for the Cowboys. (1:33)

FRISCO, Texas -- Mike McCarthy's introduction as Dallas Cowboys head coach will come Wednesday, but he is busy putting together his coaching staff already.

According to sources, Kellen Moore is expected to remain as offensive coordinator, while Jim Tomsula is expected to be the defensive line coach. John Fassel was officially hired as the special-teams coordinator on Wednesday.

On Monday, it was learned that Mike Nolan will be McCarthy's defensive coordinator after spending the past three seasons as linebackers coach for the New Orleans Saints.

Moore will be a holdover from Jason Garrett's staff, although there could be more individuals returning.

That, however, will not include offensive line coach Marc Colombo, a source told ESPN on Wednesday. Joe Philbin, who coached the offensive line for McCarthy in Green Bay, is expected to reunite with his old coach in the same role.

Colombo, who took over the line midway through the 2018 season and has a contract through 2021, oversaw a unit that had greatly improved pass protection in 2019 and the fifth-ranked run game.

In Moore's first year as a playcaller in 2019, the Cowboys were the top-ranked NFL offense in terms of yards per game and sixth in points per game. For the first time in franchise history, the Cowboys had a 4,000-yard passer (Dak Prescott), 1,000-yard rusher (Ezekiel Elliott) and two 1,000-yard receivers (Amari Cooper, Michael Gallup) in the same season.

While the belief is that McCarthy will call plays in 2020, several sources indicated he was impressed by Moore, who has only two seasons of coaching experience.

Fassel had been the Rams' special-teams coordinator since 2012, and he has regularly overseen one of the top units in the league. In 2017, kicker Greg Zuerlein, punter Johnny Hekker, returner Pharoh Cooper and long-snapper Jake McQuaide were named to the Pro Bowl.

"'Bones' Fassel has been an integral part of our special teams operations since before I joined the Rams in 2017," Rams coach Sean McVay said Wednesday. "His knowledge and understanding of critical game situations and his special teams play calling have helped us rank among the best in the league in those areas. Our best wishes are with John and the Fassel family."

The Cowboys' special teams struggled in 2019. Brett Maher missed 10 field goal attempts before his release late in the season. The Cowboys had the worst kickoff return average in the NFL and allowed a blocked punt in a 13-9 loss to the New England Patriots.

At different times during his tenure with the Packers, McCarthy had a substandard special-teams unit.

Tomsula had been the Washington Redskins' defensive line coach since 2017 after a nine-year run with the San Francisco 49ers that began when Nolan was the head coach. In 2015, he was the Niners' interim head coach.