City Football Group, the parent company of Manchester City, must reduce its stake in Girona if the Spanish club is to be allowed to compete in next season's Champions League, UEFA said on Wednesday.

Liga side Girona are 47 percent owned by City Group since 2017 and, after a stunning season when they competed for a period with Real Madrid for the Spanish title, are guaranteed to finish in the top four and therefore qualification for next season's Champions League.

However, UEFA's Club Financial Control Body (CFCB) sent a letter on Tuesday to football stakeholders informing of updates to multi-club rules pertaining to entry into continental-wide competitions.

The rules prevent two teams participating in the same European tournament if they have the same owner and CFCB said that this extends to cases of "decisive influence" being held by a party over several clubs, going beyond just "control" linked to holding majority shares.

City Group is not the majority shareholder of Girona, but the CFCB letter said that if a party "holds 30 percent or more of the club's total shares, the shareholders' or members' voting or economic rights", this constitutes "the capacity to exercise a decisive influence in the decision-making of a club".

Other examples cited include representing at least 30 percent of operating income -- such as through a sponsorship contract -- holding key positions in the club's structure or having transferred at least three players in the same season.

If Manchester City and Girona are both to compete in the Champions League next term, City Group will have to divest some of its share in the Catalan club by UEFA's deadline of June 3.

To avoid a hasty sale of shares, which is generally economically unfavourable, the CFCB's letter offers a temporary option to clubs in this situation, but one that is time-limited to the coming season: the transferral of the shares into a blind trust under UEFA supervision.

In the case of City Group, failure to comply will likely leave Girona -- the team that finished the lower of the two in their domestic league -- demoted to the Europa League.

In order to prevent potential conflicts of interest, UEFA's integrity rules have had to be adapted due to the rise of multi-club consortiums -- such as City Group, which has full ownership of or stakes in 13 clubs across the globe.

Last year, these rules on multi-club ownership sparked respective investigations into Toulouse and AC Milan, Aston Villa and Portuguese club Vitoria, as well as Brighton and Union Saint-Gilloise in Belgium.

European football's governing body UEFA eventually closed the three cases after "significant changes" were made within the clubs concerned to limit the influence of their investors.