Horror knee injury leaves UFC viewers wincing

UFC star Calvin Kattar suffered a devastating knee injury against Arnold Allen that forced the bout to a TKO finish.

The pair squared off inside the Octagon in the main event of UFC Vegas 63 in a featherweight fight over the weekend.

It was a highly anticipated bout that was meant to have huge ramifications for the featherweight rankings.

It ended with Arnold securing the biggest win of his career and going 10-0 in the UFC, however, it came in the most unexpected and gruesome of manners.

Just seconds into the second round Kattar suffered an outside calf kick before he collapsed to the canvas holding his opposite right knee.

Close-up footage showed just how horrific the injury was with the American’s knee dislocating in an ugly manner.

Referee Herb Dean immediately waved off the fight and awarded the victory to Allen via TKO.

While Allen was happy with the win, he was hoping to have done it in a more convincing manner.

He said: "It's bittersweet, but things were going right in the first round.

"Everything was going as I had planned, as I had trained, as I prepared [for].

"It is what it is. Hopefully, his injury is not too bad and he heals up quickly."

The unfortunate ending means that Allen will not have progressed up the rankings as much as he would have liked to with a standout win.

He added: “I wanted a performance that would stand out so I could actually ask, like, 'Look, this deserves more this that and that. But now I'm in the same boat."

With featherweight champion Alexander Volkanoski set to challenge Islam Makhachev for the UFC lightweight title early next year, there may be an opportunity at an interim championship on the horizon.

And Allen maintained he wanted that shot.

As for Kattar, he’ll be hoping the injury isn’t as bad as it looked.

The footage left many fans online cringing.

One said: “This is an ACL tear. I know from personal experience.”

Another wrote: “My knee is aching again.”

A third commented: “Woah... Don't think I've ever seen a camera angle capture a knee rupturing like this before.”

A fourth added: “Made me wince through the screen.”