Blake appeared in three games last season with Philadelphia, completing 18 of 37 passes for 126 yards, one touchdown and one interception.
The 14-year veteran likely will compete for the third-string position behind newly appointed starter Chad Hutchinson and the backup, rookie Kyle Orton.
"Right now our top two guys will be Chad and Kyle, and then Jeff will work in after that," said Coach Lovie Smith. "As we've said all along, we feel real good about the guys we have here right now."
The projected starter, Rex Grossman, suffered a broken left ankle in the Bears pre-season game against St. Louis Friday night and will be out three to four months.
For his career, Blake has thrown for 21,656 yards and 133 touchdowns. He has 99 interceptions and a 77.9 quarterback rating.