The news comes just hours after the Lions fell to Atlanta, 27-7, a disappointing and embarassing loss on national television.
Entering 2005, armed with talent at the skill positions and a quarterback in his fourth season, expectations were high for the team, but they have since stumbled to a 4-7 start.
Following Thursday's loss, a visibly drained and troubled Mariucci took responsibility for his team's inadequacies.
"I told them (in the locker room) I shoulder the responsibility for this football team," said Mariucci. "When you look at our team, it is not necessarily any one thing -- there is a multitude of things that a head coach is responsible for, whether that is the offense, the defense, the kicking game, the conditioning, the fitness level, the health on and off the field - all of it.
"All of it - that is what a head coach is responsible for."
It is assumed that if Mariucci is fired, defensive coordinator Dick Jauron would be his replacement. Jauron previously coached the Chicago Bears.
Mariucci entered Detroit in 2003 after six years with the 49ers, where he led the team to four playoff berths and two division titles.
The Lions fired then head coach Marty Mornhinweg the moment Mariucci was dismissed from the San Francisco organization. At the time, Mariucci was clearly current vice president Matt Millen's preferred coach.
Unfortunately, his reputation and success never made the trip to Detroit. Since arriving, Mariucci has won just 15 games, tallying a .35 winning percentage
Recognized as an offensive guru, Mariucci's offense stumbled to last place in 2003, 24th overall in 2004, and is currently sixth-to-last in the league in production.