Jeffery is officially questionable with his latest injury, a week after being a game-time decision in the season opener.
"We do have a next-man-up mentality, so guys have obviously been working in there (at wide receiver) and studying," Forte said on Friday, via ESPN.com. "He's a great player. We don't have another Alshon on the team, so obviously it's going to hurt."
Jeffery played 60 of a possible 77 snaps in Week 1, but never looked like he was moving at a 100-percent clip, despite catching five passes for 78 yards.
Chicago coaches could decide to sit the talented receiver this week in hopes that the nagging injuries don't linger and cause greater time missed down the line.
If the wideout can't play, or is hindered by the hamstring throughout the contest, Forte's importance grows.
After a 29-touch Week 1 (24 carries, 5 receptions for 166 scrimmage yards) Forte faces a Cards' defensive front that gave up a league-low 54 rushing yards to open the season.
"They have a lot of different looks on defense," Forte said. "They basically have a safety down there playing linebacker, and he's a lot more athletic than some linebackers are. They also do a lot of blitzes. Penetration kills run games."
It could be tough sledding if those boxes are stuffed even more by Cards defendes sans Jeffery.