Jackson went down with a noncontact injury while defending Mike White's 54-yard touchdown pass to Garrett Wilson with 5 minutes, 9 seconds remaining in the second quarter.
Jackson exited after Cruikshank had left with a hamstring injury. With Brisker already out, the Bears were down to two healthy safeties in DeAndre Houston-Carson and rookie Elijah Hicks.
"That's part of football," said defensive tackle Justin Jones. "That's why we've got guys backing up the guys we have in there. But the guys that are the next man up, you've got to make sure you're in your playbook and make sure you know what's going on in the game because you never know when your number's going to be called."
Jackson entered Sunday's game leading the Bears with 58 tackles, four interceptions, five pass breakups and two forced fumbles.
"Eddie keeps us going," said linebacker Nicholas Morrow. "He's a good leader. Obviously, he's a great player. He's always up-tempo. I hate that for him because he's a good guy and he's done a good job of keeping everybody together and keeping everybody into the games."
"It's tough," Jones said. "He's a big part of this defense. But like I said, it's next-man-up. We've got guys who watch him every day in practice, guys who sit beside him in the meetings. So you've got to make sure that you're ready to go when it's time for you to get in there. We don't expect a drop-off when Eddie goes down. That's the type of trust you've got to have in your teammates."