Arsenal lodged a complaint with UEFA over the condition of the pitch at Atletico Madrid’s Metropolitano Stadium ahead of Wednesday’s Champions League semi-final first leg.

There were concerns from the visiting side that an increased length of grass would slow down the pace of the match, while the watering of the surface increasing the likelihood of players losing their footing.

Footage circulated on Wednesday ahead of the game showed Arsenal ground staff members speaking with the UEFA delegate.

UEFA’s competition rules state that the height of the grass must not exceed 30mm (1.18 inches) and the entire playing surface must be cut to the same height. The height of the grass must be the same for both the training sessions and the match.

UEFA or a third party mandated by the governing body of European football, which organises the Champions League, may carry out inspections of the pitch before and during matches to determine whether it is suitable.

Atletico’s pitch being watered ahead of kick-off against Arsenal (James McNicholas)

The Athletic have approached Atletico Madrid and UEFA for comment.

It is not the first time the surface at Atletico’s stadium has been the subject of attention, with multiple high-profile incidents of players slipping on the turf in recent months.

What similar incidents have happened?

In February’s Copa del Rey semi-final at the stadium, when Atletico defeated Barcelona 4-0, the scoring was opened by an own goal from the visiting side’s defender Eric Garcia, whose backpass rolled under the foot of Barcelona goalkeeper Joan Garcia and into the net.

In March’s Champions League last-16 tie in the Spanish capital, Tottenham Hotspur goalkeeper Antonin Kinsky lost his footing twice in the early stages with both errors leading to goals, while centre-back Micky van de Ven also slipped directly in the build-up to a goal.

After the match, Atletico forward Antoine Griezmann said, via AS, that Atletico “took advantage of some of their mistakes, the pitch was very slippy, and we’re more used to it”.

In February, Atletico captain Koke complained about the surface after a home defeat to Real Betis. “The truth is it’s not good, we were slipping over, (the turf) comes up,” midfielder Koke said, via Marca.  “For a team like Atletico, we need the pitch to be good to play.

Ahead of Barcelona’s quarter-final second leg in the Spanish capital earlier this month, the visiting side’s head coach Hansi Flick discussed the pitch with a UEFA delegate during his side’s training session in the stadium ahead of the game, according to sources with knowledge of the matter.

Barcelona sources briefed on the situation, speaking on the condition of anonymity, said that they were concerned about the quality of the pitch after that training session and regard it as being in a worse state than in their February meeting at the Metropolitano. The club did not make a formal complaint to UEFA, however.

Atletico sources said that the length of grass is always kept at the appropriate level, adding that the pitch has improved since the start of the year and is not, and has never been, an issue for teams playing at the stadium.

What are the rules?

Article 34.4 of UEFA’s Champions League regulations states: “The home club must respect the pitch-cutting guidelines for natural grass pitches. The height of the grass must not exceed 30mm and the entire playing surface must be cut to the same height. The height of the grass should be the same for both the training sessions and the match.

“If deemed necessary by the referee or the UEFA match delegate, the home club may be required to reduce the height of the grass for the match and training sessions.”

Article 34.5 of the same regulations adds: “The pitch-watering schedule must be communicated by the home club at the organisational meeting. The pitch must be watered evenly and not only in certain areas. As a general rule, pitch watering must finish 60 minutes before kick-off. However, upon the decision of the home club, pitch watering may also take place after that time:

1. between 10 and 5 minutes before kick-off; and/or
2. during half-time, for a maximum of 5 minutes.

“The referee is entitled to request changes to the pitch-watering schedule.”

UEFA or a third party mandated by the governing body may carry out inspections of the pitch before and during matches to determine whether it is suitable. The rules also state that watering of the pitch must conclude an hour before kick-off, though the home club can decide to allow further watering between 10 and five minutes before kick-off and for a maximum of five minutes during half-time.

“The home club must make every reasonable effort to ensure that the pitch is in the best possible condition for play. If the climatic conditions so require, facilities such as pitch heating and a pitch cover must be provided to ensure that the field of play is in a suitable condition on any match date.”