That's orthopedic sports surgeon, Dr. David Abbasi ... offering his medical opinion on Nick Chubb's gruesome knee injury, sustained during the first half of the Browns vs. Steelers Monday Night Football game.

Abbasi is a double board certified fellowship trained ortho surgeon specializing in shoulder, elbows, and knees ... and although he hasn't treated 27-year-old Chubb, he has been the sideline physician for the Miami Dolphins, Cincinnati Bearcats, FIU Panthers and a bunch of big UFC fights.

The Browns have not yet announced the specifics of the injury to the 4x Pro Bowler, but Abbasi says it's clear there was a knee dislocation, and with that, serious ligament damage.

"You can see he gets hit on his knee. That is his knee dislocating out," the doctor explained, "His knee popped out of place."

Thankfully, Abassi says the knee went back into place moments later ... and that's important because it limits the risk to the nerves and the blood vessels "which can be limb threatening."

The bad news ... for the knee to pop out the way it did, David says, "[Chubb] had to have torn at least two of the four ligaments, but usually it's more than two ligaments."

"The knee ligaments I'm referring to here consist of the ACL, the PCL, the MCL, and the LCL. I would not be surprised if at least three, if not all four of these have torn."

After the MNF game, Browns coach Kevin Stefanski confirmed Chubb would be out for this season.

It's not the first time the 4x Pro Bowler has dealt with a serious injury to his left knee. Back in 2015, Chubb tore three ligaments (all but the LCL) in a college football game vs. Tennessee. He missed the rest of the season but was back for '16.