Celtic manager Gordon Strachan accepted that his side had been soundly beaten in their 3-0 Champions League defeat at Manchester United.
The Bhoys came under heavy pressure for much of the game at Old Trafford, with Strachan choosing to praise United rather than criticise his own players.
He commented: "That's the best side we've played. Physically we couldn't match them and that told the longer the game went on.
"The first two goals were offside, but I'm not going to speak about them. I'm a football man and I know when we're well beaten.
"We kept taking punches and two or three of my players must have been pleased, but there were two or three who wouldn't have been.
"It's a wake-up call for all our players: if you want to play at the top level then that's what you're aiming for.
"I said to the players at the end of the game we can't be faulted for guts or determination, but we're nowhere near as good as them passing the ball."