Cleveland's Pro Bowl center broke his left leg Sunday and will likely miss the rest of the season, a potentially crushing blow to the improved Browns. Mack's loss has created a gaping hole in the middle of Cleveland's offensive line, which has been the main reason for the team's early success.
''You just don't replace that guy,'' quarterback Brian Hoyer said.
The well-respected Mack broke his fibula while blocking on a running play in the first half of Sunday's 31-10 rout of Pittsburgh. The tough-to-watch injury ended a streak of 5,289 consecutive snaps for the 28-year-old, who signed a five-year, $42 million contract in April.
Mack will undergo surgery in the next few days, and the Browns are hoping it's only a fracture and there's no ligament damage. Either way, he's out at least eight weeks, but it's probable Mack's season is over.
''It's tough,'' coach Mike Pettine said Monday. ''It's not just losing his play, but it's also an emotional letdown as well. To have a guy that just exemplified everything you're trying to get done, to lose him, it's big.''
Mack's injury was amplified by the loss of defensive end Armonty Bryant, who sustained a season-ending knee injury in the first quarter. Bryant was starting in place of injured lineman Phil Taylor and had already recorded two tackles in six plays when he tore ligaments.
Bryant will also have surgery, and his loss puts further strain on Cleveland's defensive line depth.
Pettine has preached to his players, especially the backups, to be ready in case their name is called. That's life in the NFL, where everyone is one play from getting a promotion or having their season or career ended.
''I told the team in the meeting today, we lost two warriors in Alex and Armonty, but we'll check the mail and there's not going to be any sympathy cards from around the league,'' Pettine said. ''It's the cliche, but it is truly next man up. We can't feel sorry for ourselves and I'm confident in the guys that we'll end up, whether we're promoting or bringing somebody in, that we'll put a functional group out there.''
After Mack was carted off Sunday, right guard John Greco slid over to center and Paul McQuistan came off the bench. Despite Greco making his pro debut and McQuistan coming in cold, the Browns (3-2) showed cohesion and were able to temporarily overcome Mack's loss.
It worked once, but Pettine hasn't decided if he'll stick with the same plan.
Because of Greco's inexperience at center, the Browns may keep him at guard. Pettine said Nick McDonald, claimed off waivers in August from San Diego and recently activated from the reserve/non-football injury list, is another option. McDonald has played in 16 NFL games - starting three.
''The plan right now is to practice him this week, but I don't foresee him playing this week,'' Pettine said. ''I could see in the short term that it is going to be John. But we're a mile away from making that decision.''
No matter where he lines up, Greco said he and Cleveland's other lineman intend to honor Mack by blocking as hard and moving as fast on every down as he does.
''We'll be playing for Alex as long as he's out,'' Greco said. ''Everything we accomplish this year, he's right there along with us. He's been in this thing long enough that we're including him in everything.''
It was obvious what Mack meant to the Browns after he was injured.
As he waited on a cart to be driven off, each of his teammates came over and offered support with a pat on the back, handshake or encouraging word.
Mack has always been there for the Browns, and their gesture showed they'll be there for him.
''It was just spontaneous. That shows you what the guys think of Alex and what he means to this team. He was a warrior for them. He sets a great example,'' Pettine said. ''When your best players are you hardest workers, you've got a chance to be something special.''
NOTES: Hoyer, who is in the final year of his contract, was asked whether he would sign with the Browns long-term if rookie Johnny Manziel is also with the team. His response: ''I don't think I need to say any more than I'm from Cleveland and this is where I want to be. But I also am a competitor, so I want to be somewhere where I'm playing.'' ... Rookie CB K'Waun Williams is following league protocol on concussions after being injured Sunday.