The child, who tested positive over the weekend, is a Year 9 student at St Mary's Catholic High School and his parents notified the school on Sunday evening (September 13).
The school took to social media late last night to inform parents that all Year 9 students should remain at home today (Monday, September 14) whilst staff figure out which of his classmates he has been in close contact with.
St Mary's said it will phone parents of the affected children and the youngsters will be asked to self-isolate for the required 14 day period.
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The school said most Year 9 students would be welcomed back to class on Tuesday.
The students who must stay at home today will be able to study via e-learning, said the school.
A school spokesman said: "For Year 9 parents - unfortunately we've just heard about ONE confirmed positive test for COVID-19 in Year 9, therefore we are asking that ALL Year 9 students stay at home tomorrow (Monday, September 14). Work will be available on Classcharts.
"Once we have determined who has been in close contact we will phone parents in person and will expect the majority of students to return on Tuesday.
"Apologies for any inconvenience that this may cause."
South Ribble has been identified as an area of growing concern, with 68 cases recorded in the borough since September 1.
This included 14 cases on Sunday, September 6, which is the largest number of cases in a single day since the peak of the virus in South Ribble on April 24.