Ludovic Giuly has recalled how the Barcelona team was "destroyed" by a 16-year-old Lionel Messi in training.
Then Barcelona coach Frank Rijkaard promoted Messi to the first team to make up the numbers on the training pitch during an international break.
And Giuly - who won two La Liga titles and the Champions League with Barca - was thoroughly impressed by what he saw at the time.
"Messi was only 16, but he destroyed us all in a training session," Giuly was quoted as saying by Sport.
"They were kicking him all over the place to avoid being ridiculed by this kid, but he didn't say anything. He just got up and kept on playing.
"Every play he made was dangerous. It was incredible. He would dribble past four players and score a goal.
"Even the team's starting centre-backs were nervous. They would go in hard on him, but he took it in. He was an alien. He killed us all."
Since that training session and his making Barca debut in 2005, Messi has scored over 450 goals for the club and has established himself as one of the best players in world football.
The 29-year-old has netted six times in as many outings this campaign, scoring a hat-trick in the 7-0 demolition of Celtic on Tuesday, with his treble a record sixth in the Champions League.