Middlesbrough have lodged a formal complaint with the EFL, alleging a Southampton staff member spied on their training ahead of Saturday's Championship play-off semi-final first leg. The incident occurred on Thursday, violating EFL rules that prohibit opponents from observing training sessions within 72 hours of a match. EFL rule 127, introduced after Leeds United's 2019 spying scandal involving Marcelo Bielsa, strictly bans such conduct. Leeds were fined £200,000 for the breach, which led to the rule's implementation.

The EFL is now investigating Southampton's alleged involvement, though no further details have been disclosed. Both clubs emphasized adherence to league regulations in their joint statement. The controversy could cast a shadow over the high-stakes Riverside Stadium clash, with fans and analysts questioning whether the tension will affect team focus.

Sky Sports understands the EFL will review footage and statements before issuing a ruling. This incident echoes the 2019 controversy but raises fresh questions about oversight ahead of crucial play-off matches.