The English Football League (EFL) has launched an investigation into an alleged case of spying by Southampton on Middlesbrough before they meet in the Championship play-offs.
The first leg of their semi-final takes place at the Riverside Stadium on Saturday, with the return at St Mary's on Tuesday.
BBC Sport has learned Saints' performance analyst was allegedly caught recording Boro training and taking pictures of tactics late on Thursday morning.
The staff member was caught, told to delete the footage and leave the area, but the Teesside club were furious and later contacted the EFL.
An EFL statement released on Thursday evening read: "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.
"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."
Southampton have been approached for comment.
EFL rules state "no club shall directly or indirectly observe (or attempt to observe) another club's training session in the period of 72 hours prior to any match".
It was brought in seven years ago after Leeds United were fined £200,000 by the EFL for watching opponents train before matches.
A member of Leeds' staff was found acting suspiciously outside Derby's training ground before a fixture between the two sides on 10 January, 2019.
Boss Marcelo Bielsa revealed he had sent a member of staff to watch training sessions of every team Leeds had played that season.
The EFL found Leeds breached rules over treating teams with "good faith".
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