Despite being listed as doubtful, Jennings wanted to play and it was "50-50 at this point," one source told ESPN NFL Insider Adam Schefter on Wednesday.
James Jones started at receiver in place on Jennings.
Jennings, who didn't practice all week, was put through a series of tests before Thursday's game to measure his progress.
Jennings was hurt late in Sunday's loss to the San Francisco 49ers. He had five catches for 34 yards before the injury.
While Jennings can't be replaced, the Packers at least were in position to use their three- and four-receiver packages without him. Veteran Donald Driver was available to step into the rotation after sitting all but the three plays Jennings missed in last Sunday's 30-22 loss.
An increase in playing time would be welcome news for the 37-year-old Driver, who told reporters Tuesday he was disappointed by his lack of activity in the opener.
"I didn't go into that game thinking I wasn't going to play," Driver said, according to the Green Bay Press Gazette. "The way it came out, I didn't. It sucks, but that's the way it goes."
Jennings also missed time in the preseason because of a concussion. The 2012 season is pivotal for Jennings, whose contract expires at the end of the season.
And although it's only Week 2, history says the Thursday night game at Lambeau Field might be pivotal to the Packers' playoff hopes. According to ESPN Stats & Information, only two teams in the Super Bowl era (since 1966) have started 0-2 -- with both losses coming at home -- and still made the playoffs: the 2003 Eagles and the 1987 Colts. In addition, a Packers loss would mark just the third time in this era that the franchise would have opened a season with consecutive losses at home (1988, 2006).
Tillman was unable to finish against the Colts and missed practice on Tuesday, but did have limited participation in Wednesday's walk-through practice. Tillman has skipped only six games over the past seven years.
Other Bears' inactives include: defensive tackle Nate Collins, defensive tackle Matt Toeaina, safety Jeremy Jones, offensive tackle Jonathan Scott, wide receiver Dane Sanzenbacher, tight end Kyle Adams and offensive lineman Edwin Williams.
Information from ESPN NFL Insider Adam Schefter, ESPN's Rachel Nichols, ESPN.com NFC North blogger Kevin Seifert, ESPNChicago.com's Jeff Dickerson and The Associated Press was used in this report.