Cristiano Ronaldo converted a penalty kick in Wednesday's 3-1 win over Paris Saint-Germain with what was effectively a volley.
Ronaldo disturbed the turf under the ball, which made it move up to create a volley effect.
Rio Ferdinand, speaking in his role as a pundit for BT Sport, said: "He used to do that in training, you know.
"He used to mess about in training and do it but to do it in a game. I'm not saying he means it but he used to do it, I swear to you.
"Crazy, but he used to do it."
Former Premier League referee Graham Poll told the Daily Mail: "You cannot blame the officials for missing it, as it would have been almost impossible to spot in real time.
"But with the benefit of slow-motion replays, we can see that the ball bobbled up as Ronaldo planted his left foot before slamming it home with his right."
Ronaldo's penalty. The ball pop up before he takes it. Wow. pic.twitter.com/oIDzw28JrG
— Arsenal Related ⚽🔥 (@ArsenalsRelated) February 14, 2018