"That's a humbling experience for us," McGregor told TNT after doubles from Alvaro Morata and Griezmann, along with goals from Samuel Lino and Saul Niguez.

"It's embarrassing to concede six goals. It's hard enough at this level with 11 men. That's two games we've had players sent off.

"If we can get to 1-0 at half-time, the game probably feels a little bit different. We make the game difficult for ourselves.

"We played really well in the game two weeks ago, but that's a sore one for us."

Celtic were already trailing to a deflected strike from Griezmann when Maeda had a yellow card upgraded to red.

The Japan forward raised his leg in a 50-50 challenge with Mario Hermoso, who caught his opponent's studs as he followed through.

"The red card is a big turning point," Rodgers said. "We started with confidence, then get a man sent off early, which was a huge disappointment.

"When you watch the re-run, both players kick each other's feet.

"The ref saw it in game time and didn't deem it worthy of anything so serious, but it just feels like a computer game now, football. So many visits to the screen, so many influences in the game.

"It's not so much the technology but how it is implemented. It's not something I enjoy."

With one point from four outings, Celtic are not yet eliminated, although they will need to beat Lazio away and Feyenoord at home - and rely on Atletico doing them some favours.

"We knew we had to take something from this game, but with Lazio winning as well, our objective with two games to go is to get points and see if we can improve on last season's points total," Rodgers said.

'Very difficult to watch'

Celtic are without a win in their last 14 Champions League group stage matches (D3 L11), a run that dates back to September 2017.

A last-gasp defeat at home to Lazio was hard to take, while a stirring 2-2 draw at home to Atletico earned praise.

However, this was a big step backwards, even when a harsh red card and yawning gulf in budgets is taken into account.

"For Celtic, it is not good enough to lose 6-0 away from home," former Celtic winger Aiden McGeady told BBC Sportsound.

"Being a little bit more reserved, it might not have finished 6-0.

"But Brendan is a manager that sticks to his principles and sometimes you learn the hard way. It was very difficult to watch.

"I was surprised by the formation and the substitutions.

"In the last half an hour or so, it looked like Celtic were still trying to attack and Atletico were able to capitalise on the space that created."

Rodgers stuck with a 4-3-2 formation after the loss of Maeda, with Oh Hyeon-gyu coming on at half-time.

"You have seen my teams enough back home," the manager added. "Whenever we lose a man, it's having that structure.

"Listen, you can have any structure you want, it can be very, very difficult against that level of opponent. It just didn't work for us, so we have to take our medicine."