要点如下：

Explaining injury emergency signing rule

The [[NEWS.CONTENT_HTML]]quot;injury emergency signing[[NEWS.CONTENT_HTML]]quot; rule in La Liga allows clubs to sign a replacement player if someone is injured for more than four months. The signing must be a free agent or a player from within Spain, specifically La Liga or Segunda. Historically, this rule was for injuries lasting over five months, but I think it has changed recently to four months. The RFEF used to allow emergency signings for goalkeepers at any time, but for outfield players, medical committee approval is needed.Clarifying injury signing rules

The news line refers to [[NEWS.CONTENT_HTML]]quot;超四个月,[[NEWS.CONTENT_HTML]]quot; meaning exceeding four months, but historically, the threshold has been five months. I recall that Barcelona signed Martin Braithwaite in February 2020 when Ousmane Dembélé was sidelined for six months due to a hamstring injury. They paid the release clause, and I think the rule requires a player to be out for at least five months. Another example is Gavi from Barcelona, who had a torn ACL, but they may not have signed anyone due to financial fair play. So, the threshold is indeed five months.Investigating injury exception threshold

The article mentions the threshold as four months, which suggests that the RFEF may have recently changed this, possibly in 2024. I need to be cautious since the user's reference to [[NEWS.CONTENT_HTML]]quot;Mundo Deportivo[[NEWS.CONTENT_HTML]]quot; indicates that if Christensen's injury exceeds four months, Barcelona can use the injury exception. I remember that historically, the threshold was five months, but some reports suggest it changed after a 2023 RFEF circular. In the 2023/24 season, the long-term injury substitution rule may indeed include four months. I think Real Madrid also considered signing a goalkeeper after Courtois’ injury.Explaining Barcelona's registration situation

In 2023, Barcelona received approval to register Vitor Roque due to Gavi's long-term injury. They didn't sign him outside the transfer window but registered him early, using the allowance to replace a long-term injured player for squad registration. This also can influence salary cap limits, permitting them to spend up to 80% of the injured player's wages on a replacement, provided the injury lasts at least five months. The replacement can only play domestically and must fill an equal role.Outlining signing conditions

It’s true that emergency signings outside the transfer window can only participate in domestic competitions, not UEFA. If Christensen is out for more than four months, here’s a brief overview of the conditions for Barcelona:

• Injury confirmation by an independent medical committee; current minimum absence is four months.
• Options include signing a free agent or purchasing from a Spanish club, but not from foreign leagues.
• Registration is only valid for domestic competitions, not UEFA.
• Financially, they can use up to 80% of the injured player’s salary, subject to financial fair play.
• Timeline for signing is typically within a short window after approval.

Let me know if the user wants more detail or a candidate list!