Teenage Liverpool striker Michael Ngoo was booked after revealing a T-shirt tribute to the Hillsborough victims during an Under-21 match at Chelsea on Friday night.
Ngoo, 19, scored the final goal in a 4-1 Liverpool victory at Brentford's Griffin Park, then removed his shirt to reveal a message which read '96 reasons 4 justice'.
Official guidelines state that referees should show a yellow card to players who take off their shirt, but the crowd booed the booking and cheered the player.
The incident came two days after the Hillsborough Independent Panel released a report into the 1989 disaster, in which 96 Liverpool fans died.
It cleared supporters of any blame for the tragedy, and showed evidence of a cover-up by police and ambulance officials.
Steve Hunter, a journalist for Liverpool's official website, showed his support for Ngoo by tweeting: "Really enjoyed the U21s game, the lads did brilliantly 0 and Michael Ngoo, a lovely gesture. He's a great lad is Michael."
Ngoo joined Liverpool from Southend in 2009, and played for England at the Under-20 World Cup in Colombia in 2011.