The mystery surrounding a high-school football coach’s sudden disappearance in the middle of an undefeated season has deepened after the school district revealed an unidentified staff member was placed on leave over an ongoing probe.

Travis Turner, the head grid coach at Union High School in Big Stone Gap, Va., was still listed as a missing person on the Virginia State Police database as of Monday after he vanished late last week, cops confirmed to The Post.

Police had earlier disclosed they were en route to the 46-year-old’s home in Appalachia on Thursday as part of the “early stages of an investigation” when he went missing.

Virginia HS Football coach Travis Turner is missing amid an undefeated season — and a mysterious police probe. Virginia State Police

Travis Turner (right), the head grid coach at Union High School in Big Stone Gap, Va. Facebook/Leslie Turner

Turner’s wife, Leslie Caudill Turner, wrote Friday that the coach was missing. Facebook/Leslie Turner

Cops did not reveal what the probe was about.

“This was part of the investigation, and NOT to arrest [Turner],” police said in a statement. “While in transit, the agents were informed that Turner was no longer at the location.”

In a since-deleted Facebook post obtained by News Channel 11, Turner’s wife, Leslie Caudill Turner, wrote Friday that the coach was missing, “and that’s all we know.

“We love him and need him here with us,” she said. “Just keep praying that he comes home.”

The same day, officials at Wise County Public Schools — which oversees Union High — disclosed that an employee within the district had been placed on administrative leave.

Neither they nor cops would identify the person, including whether it was Turner or if the two cases were connected.

A recent football game at the local winning team’s Phil Robbins Field is packed with spectators. Union High School/Facebook

Turner’s disappearance comes amid what should be a celebratory undefeated season for his team. Facebook/Leslie Turner

The school’s assistant coach, Jay Edwards, has since stepped in to handle all coaching responsibilities. Leslie Caudill Turner / Facebook

“A staff member has been placed on administrative leave with pay while an external agency reviews an allegation that was reported to the division,” the district said in a statement without elaborating further.

“This is standard procedure and not a determination of wrongdoing. This situation also involves an active law-enforcement matter, and the division cannot comment further.”

A state police rep only said in a statement, “Virginia State Police has utilized a number of assets, including search and rescue teams, drones and k9s, to assist in the search, and hopefully, locate Turner safely.

“At this time, Turner has not been located. The investigation remains ongoing.”

Turner’s disappearance comes amid what should be a celebratory undefeated season for his team.

The school’s assistant coach, Jay Edwards, has since stepped in to handle all coaching responsibilities as the missing-person probe continues.