Each player provides a unique skill set for the offense, and arguments could be made one of the running backs could carry a full workload.
"The fact of the matter is we're going to go running back by committee," McCarthy told Rob Demovsky of ESPN's NFL Nation. "But if one of them would emerge as that full-time guy then you have to have that ability to ... adjust to that.
"As far as planning and going into the season, that's why we're going about it that way. We feel like we've got three guys that have all done it, but they haven't done it over a long period of time, so I think it's just practical thinking from that position and realizing that it's a very demanding position."
Given McCarthy's current stance, the Packers have options to build a running game with a view to a committee approach after finishing the 2017 season ranked 17th in the league (107.8 yards rushing per game).
Of the trio, the 25-year-old Montgomery provides the most experience as he enters a fourth season. Montgomery appeared in eight games with five starts in 2017, and totaled 273 yards rushing and three touchdowns on 71 carries, averaging 3.8 yards per carry.
Williams, 23, appeared in all 16 games (seven starts) and led the Packers in rushing with 556 yards on 153 carries (3.6 yards per carry) in 2017, and his four rushing touchdowns tied with Jones as most on the team. Williams also led the backfield with 25 catches for 262 yards and two touchdowns.
The 23-year-old Jones, who appeared in 12 games (four starts), offers the most explosion out of the backfield, as he totaled 448 yards rushing on 81 carries, averaging 5.5 yards per attempt in 2017.
While each running back could carry the load if called upon, the Packers apparently won't rely on a single rusher over the long haul given the physical stresses of the position.
"You've got to be honest about that position; there's not too many guys that can play 19 games," McCarthy told ESPN. "To be the workhorse and do it week in and week out for 19 games, you're a unique player. Your availability is at the top of the line because that's such a demanding position."