McCarron injured the knee in the second quarter of Saturday's 37-17 preseason loss to Miami. He grabbed his knee after handing the ball off to running back Qadree Ollison. As he completed his typical post-handoff movement, McCarron clutched the knee.
He tried to make it to the sidelines, but trainers and doctors examined him first on the field and then on the sidelines before he made his way to the locker room. He was replaced by undrafted rookie Feleipe Franks, who he had been in a competition with for the backup role behind starter Matt Ryan, who has not played at all this preseason.
After Saturday's loss, Falcons coach Arthur Smith couldn't contain his sympathy for the veteran.
"I really feel for AJ McCarron," Smith said. "Any time something like that happens and it's non-contact, it's tough when you know what these guys put into it. I feel for AJ. We'll obviously get the MRI to confirm, but he's heartbroken.
"He had bounced back and he was out there fighting, fighting for his team and trying to get the extra yards."
McCarron completed 3 of 6 passes for 43 yards. He also had one run for 7 yards before being tackled by Miami linebacker Sam Eguavoen -- the play right before he grabbed his right knee.
For the preseason, McCarron completed 8 of 18 passes for 79 yards and one interception.
With McCarron out, that leaves two quarterbacks on Atlanta's roster -- Ryan and Franks. Smith indicated Saturday night if McCarron were to be out for a long time, the team would look into acquiring another quarterback.
Among the options in free agency are former first-round picks Blake Bortles, Robert Griffin III, who recently joined ESPN as an NFL and college football analyst, and Josh Rosen. It's also possible other quarterbacks could become available in the next three days as teams have to cut down to 80 players by Tuesday afternoon.