A spokesman for the Foreign Office described the sentence as "grotesque," the BBC reported Thursday.
Noting that London was "deeply concerned," he said such punishment was "prohibited under international law."
On Wednesday, Amnesty International condemned the sentence as "torture" and said it shouldn't be carried out.
Saudi media have reported the court levied the sentence against Ali al-Khawahir, who was 14 when he stabbed and paralyzed his best friend 10 years ago.
The Islamic law of qisas, or retribution, has reportedly been interpreted by the judge in the case to mean al-Khawahir could be paralyzed as punishment.
Al-Khawahir has been in prison since the stabbing and reportedly has been sentenced to be paralyzed if he cannot come up with $266,000 to compensate his victim.