"He's actually in an appointment and all the information's not in yet," coach Mike McCarthy said on Monday afternoon, about an hour before ESPN.com's Adam Schefter broke the news via Twitter. "I really don't have anything to announce there."
FOXSports.com's Jay Glazer, who has trained with Matthews, later reported that the surgery was successful.
McCarthy said only that he was "hopeful" that the injury wouldn't require season-ending surgery. So, if Matthews is out a month-plus, it's not quite the worst-case scenario. It's not far off, though, considering the importance of Matthews in defensive coordinator Dom Capers' scheme and the Packers' shaky 2-2 record.
The injury happened on Matthews' sack of Matthew Stafford on the final play of the third quarter.
"Clay's one of those guys that's going to make two or three plays a game," Capers said on Monday. "You've seen every game this year, there's been two or three plays that he makes. I told him he's going to have to stop sacking the quarterback because the last two weeks, he's injured himself sacking the quarterback."
Even while missing the second half of the Cincinnati game with an injured hamstring and the fourth quarter against Detroit with a broken thumb, Matthews leads the team in every impact category other than interceptions. He's got three sacks, five tackles for losses, four quarterback hits and two forced fumbles.
A Pro Bowler in each of his first four seasons, Matthews has 48.5 career sacks.
Not only do the Packers lose their premier playmaker, but they're also incredibly thin at the position. Nick Perry and Mike Neal will be the starters. Both are coming off of strong games, with Perry tallying two sacks and a forced fumble and Neal registering a sack.
"The one encouraging thing to me is I think Mike Neal's made really good strides," Capers said. "I think you saw him play his best game yesterday. I think you saw Nick Perry play his best game yesterday. That's the nature of this business."
By snaps, according to ProFootballFocus.com's tally, Matthews has played in 197, followed by Perry's 186, Neal's 162 (which includes defensive tackle). Undrafted rookie Andy Mulumba has played in only 31 snaps and rookie sixth-round pick Nate Palmer has been inactive in three of the first four games and played only on special teams in his one game on the roster.
"I think Mike Neal did an exceptional job yesterday," McCarthy said. "He even went inside and played well, too, so clearly probably one of Mike's better performances in his career here. And I thought Nick did an excellent job, too, with his opportunity -- was productive. We have guys that have experience, played games for us."
So, the Packers reach a key part of the schedule without their game-changing defender. Green Bay plays at defending Super Bowl champion Baltimore on Sunday. After a home game against Cleveland, the Packers play at Minnesota, host Chicago and host Philadelphia.
"You just never know from one play to the next," Capers said. "You can have one guy out of there and the other guys have to step in and perform. You guys know that we've had that here over the years. Our Super Bowl year, the number of guys that had to step in and perform and it's just expected that everybody's going to count on you to do your job. Yeah, not knowing the status and what's going to go on there, we need for Mike Neal and Nick Perry to be ready to play next week the way they played this week. Because they played their best football this week."
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Bill Huber is publisher of Packer Report magazine and PackerReport.com and has written for Packer Report since 1997. E-mail him at firstname.lastname@example.org, or leave him a question in Packer Report's subscribers-only Packers Pro Club forum. Find Bill on Twitter at twitter.com/PackerReport.