Joel Matip was left out of Liverpool FC's squad for the 1-1 draw with Manchester United on Sunday afternoon following confusion as to his status with the Cameroon national team. Although Matip was not selected for Cameroon's final 23-man squad for the African Cup of Nations, and purportedly retired from international duty after his last appearance in 2015, his club are yet to receive confirmation as to whether it would be on the receiving end of sanctions should it choose to select him.

The rules governing the release of players to association (international) teams are found in Annexe 1 of FIFA's Regulations on the Status and Transfer of Players.

The starting point is that clubs are obliged to release their player if they are called upon by the association concerned:

"Article 1 - Principles

  1. Clubs are obliged to release their registered players to the representative teams of the country for which the player is eligible to play on the basis of his nationality if they are called up by the association concerned. Any agreement between a player and a club to the contrary is prohibited."

Article 3.1 of Annexe 1 states that the player, in this case Matip, is also obliged to respond affirmatively when called up by his respective association:

"Article 3 - Calling up players

  1. As a general rule, every player registered with a club is obliged to respond affirmatively when called up by the association he is eligible to represent on the basis of his nationality to play for one of its representative teams."

Article 4 of Annexe 1 does however provide an exception for when the player is injured:

"Article 4 Injured Players

A player who due to injury or illness is unable to comply with a call-up from the association that he is eligible to represent on the basis of his nationality shall, if the association so requires, agree to undergo a medical examination by a doctor of that association's choice. If the player so wishes, such medical examination shall take place on the territory of the association at which he is registered."

Jurgen Klopp's selection headache is arising out of the provision at Article 5 of Annexe 1 that a player is not entitled to play for the club during the period for which he should have been released. Article 5 states:

"Article 5 Restrictions on playing

A player who has been called up by his association for one of its representative teams is, unless otherwise agreed by the relevant association, not entitled to play for the club with which he is registered during the period for which he has been released or should have been released pursuant to the provisions of this annexe, plus an additional period of five days."

In the case of the African Cup of Nations, this encompasses 14 days before the first match of the competition until no later than 48 hours after the end of the country's involvement. Should Cameroon reach the final, this could see Matip side-lined until Tuesday 7 February, missing Liverpool's FA Cup replay against Plymouth, Southampton in the EFL Cup, and a number of Premier League fixtures.

When Liverpool contacted FIFA about the matter, the Press Association reported that they were informed any potential violation would be investigated by its Disciplinary Committee. Any such action could see FIFA request that the FA declare any match in which Matip appeared in contravention of the regulations and be forfeited by Liverpool pursuant to Article 6.2 of Annexe 1, regardless of the result. This could see the club crash out of the FA Cup or lose valuable Premier League points.

But what about the question of retirement?

An exception within Article 5 allows the relevant association to agree to a player representing his club during the period in which it requested his release. This would appear to suggest that a player's decision to retire from international football is only effective if their association chooses to accept it. Speaking after Franck Ribery's apparent retirement from the French national team in 2014, then UEFA President Michel Platini was quoted as saying:

"It is not the decision of the players, whether they come to the national team. This is the decision of the coach… This is defined in the FIFA statutes".

Whilst England managers have been historically co-operative with their ageing stars wishes; it would have been interesting to see whether the Argentine Football Association would have been so accommodating, had Lionel Messi not reversed his retirement.

For Liverpool, in the absence of any form of agreement from FECAFOOT (the Cameroon association) that Matip is free for selection, it is a case of awaiting FIFA intervention. This is scheduled for Friday, whether Matip returns from injury in the meantime remains to be seen