He is being held at Swansea Central police station, South Wales Police said.
The comments appeared on the Twitter account @liamstacey9, which has since been taken down.
While the feed was still visible comments claimed that his account had been hacked.
Other users of the micro-blogging service responded with outrage to the remarks.
Muamba, 23, was rushed to hospital after suffering what appears to have
been a heart attack on the pitch before 36,000 horrified spectators last
He is currently in critical condition in hospital.
The footballer's illness has prompted a wave of support and prayers from both fans and others in the world of football.
A police spokesman said: "South Wales Police have arrested a 21-year-old
male from the Pontypridd area in connection with racially offensive
comments made on the social media site Twitter.
"The male is currently being held in custody at Swansea Central Police station. There is no further information at this time."
Both Swansea University and Treorchy RFC, where the suspect is believed
to have played rugby, have made statements condemning the comments on
his Twitter feed.
"We disassociate ourselves from any racist remarks," a Swansea University spokesman said.
"We are an equal opportunities university and will be looking into this
matter. We will of course cooperate fully with any police
Treorchy RFC said it was "aware" of the comments made by the player.
"The club wishes to completely disassociate itself from these comments
and will be carrying out a full investigation into this matter," it said
in a statement.
"The club values its position and reputation within the local community
and the wider rugby community and at all times encourages our members to
treat others with dignity and respect."
In: Regional News
Tags: uk, socialist, hell hole, nanny state, racism, free speech, arrested, police state, prison, occupy, left wing, leftsit utopia, lol
Location: United Kingdom (UK/GB) (load item map)
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