Middlesbrough remain furious with Southampton after catching a man they believe is a member of Tonda Eckert’s backroom staff allegedly spying on a vital training session before Saturday’s Championship playoff semi-final first leg at the Riverside Stadium.

Boro have reported the incident to the English Football League, as spying on opposition training is in breach of their regulations. The EFL is investigating the alleged misconduct and, as of Friday, were still waiting for an explanation of what happened from Southampton. Boro want the disciplinary process to be expedited but, as things stand, expect Saturday’s game to proceed as planned.

If the EFL charges Southampton with misconduct it is understood that Steve Gibson, Boro’s owner, will expect the south-coast club to receive a severe sanction. Under a rule introduced to deal specifically with spying in 2019, such cases are dealt with by an independent disciplinary panel, which has the power to impose a wide range of punishments, ranging from reprimands to fines, points deductions and, in extreme cases, expulsion from the competition.

Southampton have 14 days to respond to allegations that one of their employees was caught filming Kim Hellberg, Boro’s manager, taking training at the club’s Rockliffe Park base near Darlington after being spotted hiding in bushes. It is understood Middlesbrough possess CCTV footage of an incident that concluded with the man they allege is a Southampton first-team performance analyst entering a toilet at the adjacent Rockliffe Hall hotel and re-emerging with a changed appearance.

EFL regulations state that the 14-day timeframe can be “abridged” in exceptional circumstances but, with St Mary’s due to host the second leg on Tuesday night, accelerating the disciplinary process presents a tricky logistical challenge. Moreover, should the EFL charge Southampton and an independent disciplinary panel find them guilty, subsequent sanctions could be informed by two wildly differing precedents involving the former Leeds manager Marcelo Bielsa and the former Canada women’s coach Bev Priestman.

In 2019, Leeds were fined £200,000 and reprimanded after a member of Bielsa’s staff was spotted watching Derby train ahead of a Championship match against Frank Lampard’s then side. At that time, the EFL had no specific anti-spying rule but found Leeds had breached regulation 3.4 that states clubs must act “with utmost good faith” towards each other. After ‘Bielsa-gate’ it introduced the new rule stating: “No club shall directly or indirectly oversee [or attempt to observe] another club’s training stadium in the period of 72 hours prior to any match scheduled to be played between those respective clubs.”

In 2024, Priestman and two other Canada women officials were banned from football for a year by Fifa after being found guilty of using drones to spy on opponents at the Paris Olympics. Canada, gold medallists at the previous Olympics in Tokyo, were also docked six Olympic group stage points. Priestman, previously England Women assistant manager during Phil Neville’s tenure with the national team and widely acknowledged as among the most talented coaches in the women’s game, was subsequently sacked by Canada and now works in New Zealand managing Wellington Phoenix.

Southampton have enjoyed an impressive improvement since Eckert, a 33-year-old former Germany men’s analyst, took charge last November. They are unbeaten in their last 19 Championship games and beat Arsenal to reach the FA Cup semi-finals. Were any misconduct charges upheld against the club it would arguably become impossible for any of their recent results to be regarded as fair.

Although Boro officials forced the alleged spy, thought to be in his early 20s, to delete the mobile phone footage he had filmed, the club remain concerned he had the chance to watch Hellberg’s dead-ball routines. Also, Saturday’s gameplan will be influenced by the availability or otherwise of Hayden Hackney. The Championship’s outstanding midfielder has recently recovered from a calf injury, but Hellberg has kept his chances of involvement against Southampton a closely guarded secret.

Boro had asked fans to line the approach roads to the Riverside Stadium and welcome their team bus with applause and flag-waving before kick off on Saturday. Southampton’s coach will make the same journey and can expect a rather more hostile reception on a day with the potential, in the words of one insider, to turn “venomous”.

Southampton have been approached for comment.