Charlotte Spink, a press officer for Merseyside police in Liverpool, said the suspect was a 59-year-old from north Wales. She did not name him. He has not been charged.
Police earlier said hate crimes officers were involved in the investigation.
They appealed to the public to help identify a man who appeared to be making a racist gesture and said Liverpool Football Club was cooperating with the probe.
It was the first time Liverpool had played Manchester United since Liverpool's Luis Suarez was suspended and fined for racially abusing Manchester United defender Patrice Evra in October.
Suarez was suspended for eight matches and fined £40,000 ($63,000), England's Football Association announced in December.
Evra said Suarez repeatedly shouted a racial slur at him during the October 15 match and demanded that Suarez be held accountable.
Liverpool issued a statement saying it was "very surprised and disappointed" with the decision.
Suarez did not specify what he said, but said it wasn't offensive.
"I didn't insult him. It was only a form of expressing myself. I called him something his own teammates from Manchester call him," Suarez said, according to the Uruguayan newspaper El Pais.
Suarez is from Uruguay. Evra was born in Senegal and plays international soccer for France.
The commission found that Suarez "used insulting words towards Mr. Evra" and that those words "included a reference to Mr. Evra's color," the FA statement said.
Saturday's arrest is the second time this month that a person at a Liverpool match has been accused of racism
Earlier this month, Merseyside police arrested a 20-year-old man on "suspicion of a racially-aggravated public order offense" following a Liverpool match against Oldham.
The team made a public apology after Oldham defender Tom Adeyemi complained of being abused by Liverpool fans during a January 7 match.
"All of us are deeply sorry for what happened on Friday night and players and our club pass on our sincere regrets to Tom Adeyemi for the upset and distress he suffered as a result of the matter at hand," the club said in a statement on its website.
Liverpool is not the only top-flight English soccer team to face allegations of racism.
Chelsea's John Terry -- who is also captain of the England team -- has been charged by police for allegedly racially abusing Queens Park Rangers player Anton Ferdinand, and will face a court case in February.
| Posted: at | |
TRENDING GISTS 
Watch Touching Video Of Lady Surprising Boyfriend Who’s An Okada Rider
Sports Minister, John Enoh Roots For Peseiro’s Return To Super Eagles
Just in: EFCC Withdraws Suit Against Yahaya Bello In Appeal Court Over Alleged Fr@ud
Federal Govt Suspends Dana Airline Indefinitely Over Safety Concerns
PHOTOS: How Four Friends Died In Akwa Ibom Auto Crash