Executive principal Genevieve Simson said the Wanganui Campus would be closed for at least the next 24 hours.
"As a precautionary measure, the Wanganui Campus at Greater Shepparton Secondary College will be closed for 24 hours initially, or until we receive advice it can re-open," she said.
"The campus will be closed to all students, staff and members of the community."
She said all staff and students must remain at home for the "initial closure period" while the Department of Health and Human Services undertakes contact tracing.
"This includes limiting movements to home-based activities and not attending public places," Ms Simson said.
"We will provide further information following confirmation of advice from the Department of Health and Human Services."
Ms Simson said Mooroopna and McGuire campuses will remain open for on-site learning.
It is not known whether the person diagnosed with COVID-19 is a student or a teacher.
All three Greater Shepparton Secondary College campuses have required visitors to leave their contact details for the purposes of contact tracing for about a week.
She said she was aware it was a time of "heightened anxiety", and any questions could be directed to the Department of Education and Training staff on the coronavirus hotline on 1800 338 663, which is operational 8am to 6pm, seven days a week.
All schools across Victoria returned to remote learning on Wednesday, except vulnerable students and children of essential workers, and specialist school students in regional Victoria.
Greater Shepparton has eight recorded active cases of COVID-19.
