However, the source said Sunday evening that surgery has not been ruled out. If Matthews does need surgery, he could miss several games.
Matthews was injured on the final play of the third quarter, when he sacked Lions quarterback Matthew Stafford for a 12-yard loss. Matthews rushed off the edge and was unblocked on the play, which was his final snap of the game.
Team doctors took Matthews into the locker room shortly after the play. He was not in the locker room during the postgame media access.
It is possible that Matthews would be able to play with a protective cast. But if he needs surgery to repair the break, then that is probably unlikely.
The Packers made no official announcement about Matthews. The source said the team should know by Monday whether Matthews can get by without having surgery.
It was the second straight game in which Matthews dropped out with an injury. He missed the second half of the Packers' Week 3 loss at Cincinnati because of a hamstring injury. He used last week's bye to recover and returned to start against the Lions, recording five tackles, including a tackle for a loss, and a sack in three quarters.
In Matthews' absence, Mike Neal and Nick Perry finished the game at the two outside linebacker positions. Neal replaced Perry in the starting lineup and had one sack. Perry responded with his first career two-sack game.
Matthews was one of three linebackers injured against the Lions. The Packers lost Brad Jones to a hamstring injury in the first half. Jones' replacement, Robert Francois, then tore his right Achilles tendon, the Packers announced.