Glen Kamara's lawyer claimed Sparta Prague should be 'embarrassed' by the treatment dished out to the Rangers midfielder in a stadium filled with schoolchildren.
Kamara was booed every time he got the ball months after Ondrej Kudela, of Sparta's rivals Slavia, received a 10-game ban after UEFA found him guilty of racially abusing the Rangers player.
The Letna Stadium was originally meant to be shut for the Europa League game, which Sparta won 1-0, following a separate racist charge against the club after Monaco's Aurelius Tchouameni was subjected to abuse from the stands last season.
UEFA instead agreed to a proposal for the game to go ahead in front of mainly schoolchildren with some accompanying adults, but booing was audible any time Kamara touched the ball.
The Finland international's night went from bad to worse when he was sent off in the 74th minute, to huge cheers from the crowd, after receiving his second yellow card, for what looked a harsh decision after an aerial challenge.
Kamara's lawyer, Aamer Anwar, said in a statement: "I had hoped when I heard of the stadium closure of Sparta Prague that both Glen and other black players wouldn't have to put up with any abuse or racism and could just get on with playing football.
"But this evening should be an embarrassment for the Czech side that, despite their fans being banned, it still made little difference that the stadium was filled with 10,000 schoolchildren.
"A huge proportion of those children booed Glen's every touch of the ball along with every other black player for Rangers. Tonight shows yet again that Prague has a serious problem with racism and as usual UEFA is nowhere to be seen.
"Glen and the Rangers players have shown total class, but no player should have to face this at their work and on the European stage."
On the game, Rangers manager Steven Gerrard admitted Sparta had looked the more threatening side but he was encouraged by his team's general play.
"They have had one good chance from a set-play and took it, which we will look at, and we had two very similar chances," Gerrard told Rangers TV.
"For large parts of the game we passed it very well and played with control.
"I still think we can be better around the box in terms of variety and trying to open a team up. Our keeper has been more busy than theirs.
"But when we went to 10 men and took more risks and played with more endeavour and desire, I thought we created more and still looked like we could rescue a point."
The defeat left Rangers with no points from their first two games.
"We have to win the next game at home to Brondby to give ourselves an outside chance," Gerrard added.
