Manchester City will be without key January signing Marc Guehi for their Carabao Cup final showdown against Arsenal at Wembley on Sunday. Despite other winter arrivals being eligible, the England international has been sidelined by a new rule. Pep Guardiola has been left exasperated after the former Crystal Palace defender was officially ruled out.The absence of Guehi stems from a Carabao Cup regulation implemented for the first time this season. Under the current EFL framework, if a player is signed after the first leg of the semi-final stage has taken place, they are deemed ineligible to participate in any further rounds of the competition for their new club. Guehi completed his £20 million ($27m) move from Palace to the Etihad Stadium during the January transfer window. However, by the time the deal was finalised, the semi-final stage of the League Cup had already commenced, automatically triggering the restriction that prevents him from taking the field against Mikel Arteta’s side this weekend.The situation is further complicated by Guehi's earlier involvement in the tournament with his former club. The 25-year-old actually captained Crystal Palace against Arsenal in the quarter-finals back in December. Despite City’s significant financial outlay to secure his services midway through the campaign, the governing body has remained firm on the registration deadline, leaving Guardiola without one of his premier defensive options for the season's first major final.Guardiola has not hidden his frustration regarding the situation, having previously voiced his concerns when City first booked their place at Wembley. The Catalan coach, who is known for his meticulous preparation, feels the rule is illogical and penalises clubs for their mid-season investments.Speaking about the restriction, Guardiola said: "Hopefully in March, we can arrive with the players fit and hopefully you can convince the Carabao Cup that Marc Guehi can play in the final. Because it's difficult to understand that the club who make a big investment to pay one player who belongs to us and I don't understand why he cannot play the final. So, hopefully we write a letter, and hopefully the Carabao Cup can understand. He's not able to play for a rule that I don't understand why. Hopefully, they can change it."Adding to Guardiola's frustration is the fact that fellow January recruit Antoine Semenyo is completely eligible to play. Semenyo’s involvement has already sparked controversy this season, particularly when he featured in the semi-final win over Newcastle despite having played in an earlier round of the competition for his previous club, Bournemouth. The Ghana international was instrumental in the 2-0 first-leg victory at St James' Park, helping City reach their first League Cup final since 2021. The difference between the two cases remains the date of registration: Semenyo was signed and registered early enough in the window to beat the EFL deadline, whereas Guehi's arrival came just too late to satisfy the specific semi-final cut-off point.Add GOAL.com as a preferred source on Google to see more of our reportingThe absence of Guehi comes at a precarious time for the City backline, which has already been stretched by fitness concerns. Josko Gvardiol is currently sidelined through injury, meaning Guardiola’s tactical flexibility is severely limited for the trip to Wembley. The manager will now have to choose between Ruben Dias, John Stones, Nathan Ake, and Abdukodir Khusanov to fill the void, knowing that any further setbacks could leave his defence exposed against Arteta’s Gunners. In contrast, Arsenal head into the final buoyed by their progression to the European quarter-finals, meaning Guardiola must find a way to motivate a squad that is missing both a key January recruit and its primary left-sided defender.