Jackson, who has a history of leg injuries, had to be taken off the field in a cart.
"It was a moment of silence" cornerback Macho Harris told the Philadelphia Daily News. "A situation like that, all you can do is just pray, ask God to step in his life for understanding and guidance, but man, I definitely feel his pain."
When asked who would step into Jackson's starting spot, Eagles defensive coordinator Sean McDermott expressed confidence that Philadelphia had the players to fill the void.
"We've got quite a few players back there that we have a lot of confidence in, with [second-round pick] Nate [Allen] and Quintin Demps -- Quintin's played before," McDermott told the Daily News.
Demps told the Delaware County Times that this isn't how he wanted to earn the starting free safety job.
"That's not something you want to see, man," Demps told the newspaper. "We're in deep competition, but you don't want to win a competition like that. I'm going to pray for the dude. I know he'll pull through."
Allen, who took most of the first-team snaps after Jackson's injury, said his sudden opportunity for a bigger role in the defense was bittersweet.
" ... I don't want it to be something off [an injury]. It's unfortunate. But I've just got to get in the playbook and keep preparing like I have been," he told reporters, according to The Morning Call.
Jackson, who left the Indianapolis Colts to sign with the Eagles in March, suffered season-ending knee injuries the past two seasons and had surgery on both knees.
He missed the second half of 2008 with a torn ACL in his right knee and tore the ACL in his left knee in 2009.
ESPN's Sal Paolantonio contributed to this report.