The Football Association is investigating a laser being shone at Manchester United's Wayne Rooney during the League Cup defeat by Middlesbrough.
Television footage showed a green light appearing on Rooney's face as he prepared to take his penalty.
The striker's effort was saved by Boro goalkeeper Tomas Mejias and United were beaten 3-1 in the shoot-out after the game finished 0-0 following extra-time.
The FA said it is aware of reports of the incident and is looking into it.
The penalties were taken at the end of Old Trafford housing the away supporters.
United manager Louis van Gaal said Boro were "lucky" to win the shoot-out.
"It is more like the casino, red or black," Van Gaal said. "We trained yesterday on penalties, but it is like that. I cannot take them."