TEMPE, Ariz. -- There are few, if any, tasks more daunting than the one facing the Arizona Cardinals this week.

How do they, if needed, replace David Johnson?

The All-Pro is seeking a second opinion on the left-wrist injury he suffered in Arizona's 35-23 loss to the Detroit Lions on Sunday. The early prognosis isn't optimistic. Coach Bruce Arians said it's likely a dislocated wrist, which could keep Johnson out for up to 12 weeks if it requires surgery.

While an official diagnosis hasn't been made just yet, the Cardinals are preparing for life after Johnson, whether it's temporary or permanent this season.

"There's some big shoes for somebody to step into," right tackle Jared Veldheer said. "We need good running backs in our system. We need somebody to step up."

Whoever that might be has his work cut out for him -- or them.

Johnson led the NFL with 2,118 yards from scrimmage last season and 20 touchdowns. He had 1,239 rushing yards and 879 receiving yards. He was an All-Pro and a Pro Bowler.

Talk about the big shoes that Veldheer mentioned. They're huge shoes. But the running backs behind Johnson on the depth chart feel they're prepared to take on Johnson's workload. Unless another roster move is made this week, it looks like the depth chart will just slide up a spot, meaning Kerwynn Williams will be the starter, Andre Ellington will be the backup and Eli Penny will be the third-stringer.

Arizona signed former Arizona State running back D.J. Foster off the New England Patriots' practice squad on Monday, according to ESPN's Mike Reiss.

"We feel like we can pick up the slack when a guy like David goes down," Penny said.

However, that quartet of running backs will have to get their legs ready. They combined for 370 yards from scrimmage last season -- 277 rushing yards and 93 receiving -- that's 17 percent of Johnson's total. Penny spent last year on the Cardinals' practice squad and played just one snap Sunday against the Lions.

The only running back on the Cards' roster who has any significant experience as a primary back is Ellington. He has 1,697 career rushing yards, including a career-high 660 yards in 2014 when he started all 12 games he played in. He's also the closest thing Arizona has to Johnson as far as a pass-catching running back. He has caught 114 passes for 1,034 yards in four seasons.

He's prepared to take on a larger role if called upon.

"Obviously, I've been there before," Ellington said. "I was that guy getting multiple carries. I'm ready for the challenge. I have to step up in his place. Once our brother's down, we got to make up for his slack."

If the Cardinals lose Johnson for any extended period of time, Veldheer said it's a "sock to the gut."

Replacing Johnson with just one man will be a struggle for the Cardinals, but they now have four running backs who can share the impossible task of filling in for one of the best running backs in the NFL. That's if Johnson misses any time.

"It just leaves a lot of other guys with more opportunities," Ellington said. "It's some huge shoes to fill. We're more than capable of doing it. But as an offense, we just got to pull together and execute better."