The English Football League (EFL) is investigating Southampton after Middlesbrough lodged a formal complaint over allegations of “unauthorised filming” at their training ground on Thursday.

Middlesbrough are due to host Southampton at the Riverside Stadium in the first leg of the Championship play-offs on Saturday (May 9) before travelling to the south coast for the return leg on Tuesday (May 12).

With a place in the Premier League and around £200million at stake for the overall play-offs winner, Middlesbrough alleged they spotted a Southampton official secretly filming their training session at Rockliffe Park.

A man, allegedly a member of Southampton’s backroom staff, was discovered at Middlesbrough’s training ground on Thursday morning. The person was confronted by a member of Middlesbrough’s personnel and ran off.

Boro are understood to have CCTV footage of the incident, according to people familiar with what happened, speaking on condition of anonymity.

The person was spotted as Boro head coach Kim Hellberg took first-team training at Boro’s Rockliffe Park training ground, a significant session before Saturday’s game. A Boro employee noticed someone loitering near the golf course attached to the hotel beside the training ground.

Allegedly, the person was filming using a phone with earphones connected. Confronted by a Boro employee, the person gave a brief answer before moving away swiftly towards the hotel, then returned to the golf course clubhouse to get changed. He then made for the car park and drove off.

“The EFL has written to Southampton FC requesting their observations following a complaint from Middlesbrough FC relating to alleged unauthorised filming ahead of the two clubs’ meeting in Saturday’s Championship Play-Off Semi-Final First Leg,” a statement from the EFL read.

“The alleged incident is said to have taken place on Middlesbrough’s private property by an individual identified to be associated with Southampton. The League is treating this matter as potential misconduct under EFL Regulations and will be making no further comment at this time.”

Middlesbrough and Southampton have been approached for comment.

These allegations are similar to the ones made towards Leeds United in 2019. The then-Championship club were fined £200,000 by the EFL for watching opponents train before matches.

This came after a member of Leeds’ staff was found acting suspiciously outside Derby’s training ground before a fixture between the two sides a month prior. Derby went on to beat Leeds over two legs in the playoffs at the end of that season.

Middlesbrough finished fifth in the Championship (the second tier of English football) while Southampton finished fourth. This saw both sides qualify for the playoffs. The winner of the two-legged tie will face the winner of a two-legged tie between Hull City and Millwall in the playoff final at Wembley Stadium on May 23 where the winner will achieve promotion to the Premier League.