By Chris Emma–

CHICAGO (CBS) — Ever fluent in coach-speak, John Fox so often utilizes the convenient crutch of so many of his peers.

“Next man up,” Fox said last week, has said in the past and will say over and over again about his Bears.

Coaches love this phrase. It spells out sustainability while preaching competition to the players.

Ideally, such an expression would constantly prevail. Unfortunate injury to a key player would lead to either a rising young player or established veteran depth piece entering the fold and seamlessly replacing the starter. If only there was always a Lou Gehrig to replace Wally Pipp.

Of course, the Bears aren’t exactly living in an ideal world right now.

Bears center Hroniss Grasu on Saturday suffered a potentially serious knee injury during the team’s Family Fest scrimmage at Solider Field. He was carted off after a non-contact injury created great concern. The Bears will learn more in an MRI on Grasu’s right knee late Saturday.

“I don’t know the extent of it,” Fox said of Grasu’s injury. “It looked fairly serious. But we won’t really know until the medical people take a look at it.”

That’s just part of the Bears’ injury concerns. On Friday, Alshon Jeffery (hamstring), Eddie Royal (concussion), Zach Miller (concussion) and Ben Braunecker (ankle) were all sidelined. Kevin White earned an off day, which offered a sobering reminder of how limited the Bears are offensively, with Deonte Thompson, Marc Mariani, Josh Bellamy, Cameron Meredith and Daniel Braverman stepping in as the first-team receivers.

After playing without Jeffery, White and Royal for many games in 2015, the Bears are counting on health offensively. Jeffery’s hamstring tightness wouldn’t be concerning if it was anybody but the fragile receiver who missed seven games last season with four different soft-tissue injuries.

Defensively, the Bears were without linebacker Danny Trevathan (knee) for the end of Wednesday’s practice and all of Saturday’s work. That’s considered to be a minor ailment.

Cornerback Kyle Fuller worked back from an ankle injury early in camp. When he was sidelined, Bryce Callahan was forced to take on a top cornerback role and Sherrick McManis stepped into the nickel, a position in which he badly struggled last season.

Next man up doesn’t work for these Bears — not after years of poor drafts from Phil Emery and even Jerry Angelo failing to establish organizational depth.

Bears general manager Ryan Pace was asked at the start of training camp whether he believes this was a playoff team. He quickly reminded the position of this franchise in his second year.

“From a personnel standpoint, we’ve just got to keep putting good drafts together,” Pace said. “We have to see how this draft unfolds. We’ve got to stack some good drafts. We’ve got to be accurate in free agency.”

Pace and his bright Bears brass have worked admirably in revamping this roster. It’s quite possible that this team will contend for the postseason in 2016, with names like Jay Cutler, Jeffery, White, Akiem Hicks, Pernell McPhee, Trevathan, Jerrell Freeman and more leading the way. Pace’s fingerprints are all over this improved roster.

However, no general manager can simply overhaul the 53-man roster from top to bottom in two offseasons. Football doesn’t work that way.

Successful organizations are built through the draft, the lifeblood of each NFL roster, with free agency serving as an avenue in which talent and depth pieces can be acquired.

The Bears are still at least one more offseason from establishing the kind of organizational depth that stacks up with the top tier of the NFL. For now, this is a roster that’s stronger but still lacking at many positions.

Unfortunately for the Bears, the reality is that injuries could derail their 2016 hopes. Should Jeffery, White or Royal miss games again, they don’t have the receivers to win with. Miller must produce at tight end, because Plan B isn’t promising. We’ll have to wait and see what comes for the offensive line.

Trevathan and Freeman could be studs at inside linebacker, but the Bears are an injury away from a replacement-level substitute like last season. Their lack of depth in the secondary is among the greatest concern, with cornerbacks Fuller and Tracy Porter needing to be consistent.

For the Bears to fight for the playoffs in 2016, they can’t afford even a few injuries to key players. Of course, no team benefits from injuries to key players, but some have the depth to stay afloat. The Bears off to a bad start in that regard.

Pace inherited an unenviable situation in cleaning up the mess Emery left behind. In two offseasons, he’s added talent like McPhee, Trevathan, Freeman, Hicks and more. The top of the Bears’ depth chart looks good, but they are still lacking true depth. Give it another offseason.

The Bears can’t win with the next man up. Fox might as well cross his fingers instead.

Chris Emma covers the Bears, Chicago’s sports scene and more for CBSChicago.com. Follow him on Twitter @CEmma670 and like his Facebook page.