Lee Wilkinson, 40, pleaded guilty in Newcastle Crown Court to unlawful wounding and a separate public order offense and Judge Simon Hickey warned Wilkinson to expect jail when he is sentenced Jan. 25, Sky News reported Tuesday.
"A custodial sentence is almost inevitable for such a serious offense as this, in my judgment," Hickey said.
Wilkinson was accused of biting the tip off Michael Dent's finger Dec. 6, 2011, during a fight at Harton Primary School in South Shields, England. Police said Wilkinson had previously been in a relationship with Dent's ex-wife.
More serious charges of wounding with intent and affray were dropped after Wilkinson agreed to plead guilty.