Detroit let Foster go on Monday, the same day Jansen was scheduled to take a physical with the team.
Foster was acquired before the 2007 season as part of a trade with Denver for Dre' Bly. Foster was a three-year starter for the Broncos.
Jansen was cut by the Washington Redskins on Friday and later that day said he would sign a one-year contract with the Lions if he passes a physical. He started in all but one game over seven seasons after being drafted from Michigan, but didn't play two years ago or in 2004. He had 11 starts last season.