Putting together a squad to play in UEFA club competitions can be a complex business.

Clubs can't simply name any of the players they wish. There are limits on how many they can include to play in Europe, and there are rules on how many home-grown players they must name in their squads.

Clubs can name a maximum of 25 players on their primary list, known as List A.

Eight places are reserved for home-grown players. A maximum of 17 players can be named who do not meet the criteria of a home-grown player.

Two players named in the 25-man List A must be goalkeepers.

Teams can also add players to List B, a separate squad list reserved for youth players.

The definitions of home-grown players are split into two categories: club trained and association trained.

Four places are reserved for club-trained players. If a club can't name four players who meet the club-trained criteria, they must leave an empty space in their squad for each player they can't name.

The definition of club trained is a player who between the ages of 15 and 21 was registered with his current club for three entire seasons. The nationality of the player does not matter.

For example, Rangers named Barrie McKay as a club-trained player because he was trained by the club between the seasons in which his 17th and 21st birthdays fell.

The definition of an association-trained player is one who between the ages of 15 and 21 was registered with any club, or a combination of clubs, for three entire seasons in the same association as the club attempting to name him on their UEFA squad list.

For example, this season St Johnstone could name Chris Millar, among many others, as an association-trained player. This is because Millar was trained by Celtic from the ages of 15 to 20, and Greenock Morton in the season of his 21st birthday.

There are 17 squad spaces available for non-local players. These can be filled by any player, regardless of nationality or where they were trained.

List B is reserved for young players. An unlimited number of players can be named or withdrawn from the list at any point in the season. The list simply has to be submitted by 11pm UK time on the day before a match.

Who qualifies for List B? In the 2017/18 season, it is any player born on, or after, January 1, 1996, who has been eligible to play for his club for "any uninterrupted period of two years since his 15th birthday".

Players aged 16 may be registered on List B if they have been registered with the participating club for the previous two years without interruption.

The deadlines to tell UEFA which players are on a club's squad list vary from season to season.

In the 2017/18 campaign, they were as follows:

Champions League

Europa League

In the qualifying rounds and the play-off round, a club can add one new player to List A, commonly referred to as a "wildcard".

A wildcard can be used to register one new player up until 11pm UK time on the night before a first leg tie in any round.

If a club has a vacant spot, they can simply add the wildcard player in. If the squad is full, a player must be swapped out.

Clubs must ensure that by using a wildcard, they still respect the requirement to have eight home-grown players in their squad. The player must also be eligible to play at domestic level at the time he is named on List A.

For games in the knockout stages of either the Champions League or Europa League, a club can register up to three new players.

The new players must be communicated to UEFA by 11pm UK time on February 1. Squad lists are then locked in for all remaining games in the competition.

There are several guidelines clubs must follow when looking to add players.

Clubs must have two goalkeepers on List A. But if either goalkeeper is ruled out through long-term injury at any point, they can be replaced temporarily.

The definition of a "long-term injury" is one that is going to last more than 30 days. If a goalkeeper recovers ahead of schedule, they cannot return to List A until 30 days have passed.

If the replaced goalkeeper was registered as a home-grown player, the new goalkeeper does not need to be a home-grown player.

The club must provide UEFA with the necessary medical evidence of the injury.

A player can't play in a UEFA club competition for more than one club in the course of the same season. But there are exceptions.

If a player has played in the qualifying rounds or play-off round in either the Champions League or Europa League, they are free to play for any other club, in either competition, from the group stage onwards.

Players can also switch clubs for the knockout stages, in line with the rules on adding players given above.

Clubs are individually responsible for submitting their squad lists. The lists are then sent to their national association to be signed, verified and sent to UEFA.

All players must have also undergone a medical, with confirmation from a doctor it has taken place, in line with UEFA's medical regulations.

Clubs are responsible for ensuring they only field players who are eligible to play.

There have been high-profile mistakes in recent years. Legia Warsaw were forced to forfeit their Champions League qualifier with Celtic after fielding a player who was suspended.

The UEFA administration decides on questions of player eligibility. Challenged decisions are dealt with by the UEFA Control, Ethics and Disciplinary Body.

You can also access open databases, compiled by STV, of all of the squads submitted by Scottish clubs to UEFA in the 2017/18 season.