
Chelsea have been blocked from naming a key player in their Conference League final squad against Real Betis due to a little-known UEFA rule.
Chelsea, who qualified for the Champions League on the last day of the Premier League season, face Betis in tonight's Conference League final.
The Blues will be aiming to become the first team to win the Champions League, Europa League and Conference League.
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But Enzo Maresca has been dealt a blow ahead of their showdown against Betis in Wroclaw, Poland.
Per UEFA regulations, Romeo Lavia is ineligible for the Conference League final.
He was not named in the List A squad Chelsea submitted to UEFA for the competition and no alterations can be made to it.
Clubs are 'entitled to register an unlimited number of players' to List B during the season.
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The list must be submitted no later than 11pm (UK time) on the day before a match.

But Lavia does not meet all the criteria required to be named on List B in a stunning turn of events.
UEFA rules state a player can be registered on List B if they are born after January 1, 2003, which Lavia, who was born on January 6, 2004, meets.
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However, the 21-year-old falls short of UEFA's other rule.
Players must have been 'eligible to play for the club concerned for any uninterrupted period of two years, or a total of three consecutive years with a maximum of one loan period to a club from the same association for a period', according to UEFA.
Lavia has not been on the books at Chelsea long enough.
He joined the Stamford Bridge outfit in the summer of 2023 for an initial £53 million from Southampton.
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The Belgian midfielder did not spend the required time at Manchester City and Southampton despite the two English clubs being in the same association as his current team.
So, Lavia will not be available for Chelsea as they look to win the Conference League.
He made a second-half cameo against Forest last weekend and has made 18 appearances across all competitions this season.

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Speaking ahead of tonight's final against Betis, Maresca said: "The Conference League is important, and it has been important since day one of the season. The reason why is because it is the competition we are in this season. We are in the Conference League, so for us, it’s the most important competition and we have to try to win.
"If we are able to win the game, it’s a good thing because we continue to build the winning mentality - and the only way to build this mentality is to win this kind of game.
"We have won many games this season, but it’s not enough. Sunday’s game is finished, and we are all happy, but tomorrow we must show the desire to win the game."