Hampshire County Council is consulting over plans to merge Fort Hill Community School in Basingstoke with Cranbourne Business and Enterprise College.
The authority said just 39 parents picked Fort Hill as a first choice for their children in September 2017 out of a possible 145 pupil places.
Critics said the council should help the school improve instead of close it.
Hampshire County Council has already announced separate plans to build a new secondary school at the Manydown development, which is near Fort Hill, where a further 4,000 homes are planned.
Campaigner Deborah Chowney said: "I think this is about them not being able to get this school to where it should be.
"Fort Hill requires improvement and Cranbourne is inadequate, says Ofsted. You're not going to send your child to a school that's struggling."
Basingstoke and Deane borough councillor Paul Harvey, Labour, said more than 1,000 people had so far signed a petition to save the school, which has space for 750 pupils.
He said: "The county council needs to be supporting the school to become the school we all want it to be."
Stephen Reid, Conservative county councillor for Basingstoke North West, said: "It's not the county council that's proposing to do this - the governing body which runs Cranbourne and Fort Hill has instigated this consultation.
"It's very sad but I can understand the governors are taking this route because, if the parents are voting with their children's feet and only having 39 registering for next September, it would be impossible for a secondary school to attract the teachers and the quality of education that it wants.
"We have to provide a quality education locally that people want and I think the best way to do that is the new school at Manydown."
Parents and councillors have come out in support of a comprehensive school earmarked for closure.