In an update to social media tonight, School principal Therese Allen said the school would close until further notice.
She said the closure even applied to staff, VCE and VCAL students, and those that required on-site supervision.
"The closure will also allow appropriate cleaning of the school site. For the moment, while our school is closed, we will not be delivering Remote learning," she said.
"While DHHS conducts further investigation, all staff and students are asked to stay at home until further advice is provided. At this stage staff and students do not need to seek testing unless they develop symptoms."
Monday 9pm: Warracknabeal Secondary College will be closed for all of Tuesday, after being informed of a positive case.
In a statement on social media on Monday night, the school did not specify whether the positive case was in a student, teacher or other staff member.
"This case has been reported to the Department of Education and Training (DET), and the Department of Health and Human Services (DHHS) is currently undertaking further investigation," the post said.
"As a precautionary measure, Warracknabeal Secondary College will be closed for 24 hours tomorrow, Tuesday 28th July 2020, while we await further advice. The school will be closed to all students, staff and members of the community.
"All students are asked to stay at home until further advice is provided.
"Our scheduled Year 10-12 Parent teacher interviews will still be happening tomorrow. These interviews will be conducted by phone as originally planned."
"The people best placed to answer your questions are the DET staff who are supporting us. You can contact them on the coronavirus (COVID-19) hotline on 1800 338 663, Monday to Friday during business hours."
School Principal Therese Allen said she had nothing further to add on Monday night, but as other information became available the school would share it with its community."
Secondary School teacher John Bish said Tuesday had been earmarked as a student free day well before Monday night's announcement.
"We were notified this afternoon," he said.
There were no new cases reported for Yarriambiack Shire in Monday's coronavirus update, which covered the 24-hour period ending at 11.59pm Sunday.
Federation University's Wimmera Campus on Horsham's Baillie Street opened to a small number of staff and students approved to be on campus on Monday.
It followed the institution undergoing a deep clean after a staff member at the campus tested positive last week.