Marlon Mack is returning to Indianapolis. 

The Colts signed the 25-year-old running back Tuesday, keeping the 2019 1,000-yard rusher among their deep stable of running backs. Mack, a 2017 fourth-round pick, has 2,383 yards on 539 carries (4.4 yards/attempt) with 20 touchdowns in four seasons with the Colts. 

Mack became an unrestricted free agent last week.

Mack suffered a season-ending Achilles' injury on his fourth carry of the 2020 season. Coach Frank Reich was impressed with the work Mack put in during training camp, and said he "looked like lightning out there" before his injury. 

"Marlon Mack broke my heart. That sucked," general manager Chris Ballard said earlier this year. "That was hard. Really hard. And it was hard on him, but he's so tough-minded. I watched him work his butt off here all season to get back. 

"… I think he's really special as a player and I could just see a backfield of Marlon, Jonathan (Taylor) and Nyheim (Hines) and (Jordan) Wilkins be really special."

The Colts' backfield stepped up in Mack's absence last year, with Taylor (1,169 yards, 11 TDs), Hines (380 rushing yards, 482 receiving yards, seven total TDs) and Wilkins (308 rushing yards) all having productive seasons. 

But having Mack back in the picture in 2021 should only strengthen a formidable Colts rushing attack.