UEFA is considering new rules on sponsorship following a Champions League draw that saw Chelsea, owned by Russian billionaire Roman Abramovich, drawn in the same group as CSKA Moscow with whom he has major financial links.
European Union competition laws and UEFA's own club regulations forbid an individual owning a major share of two clubs in the same competition but there are no rules limiting the amount by which an individual can sponsor another club.
UEFA's chief executive Lars-Christer Olsson said on Friday: "Our licensing laws and our competition rules as well as EU laws prohibit an individual owning two clubs but we shall also look at the sponsorship issue.
"Everyone knows that sponsorship has a major effect on the management of a club and we might well have to introduce new rules on this issue. We are contacting the Russian FA for full details of who exactly owns CSKA Moscow."
Preliminary UEFA checks have shown that Abramovich does not own a controlling interest in both clubs but UEFA also say that their initial checks are "superficial". They are now ordering a more thorough investigation of CSKA's financial set-up.
CSKA Moscow, the Russian champions, signed a $54 million three-year deal to have their shirts sponsored by Russian oil company Sibneft in March, of which Abramovich is the former owner and still the major shareholder.
In the unlikely event of Abramovich being discovered to have a controlling interest in CSKA, Olsson confirmed that the Russian would have to decide which club would remain in the competition. "They could not both play," said Olsson.
"I imagine this will not be the case but if it was and one club could not take part then either we'd have a three-team group or perhaps Rangers, who lost to CSKA in the qualifiers, could come into the competition presuming it was CSKA who were pulled out.
"This is unlikely and we do not have much time because the competition starts in two weeks' time. However, that is the logical conclusion if there was a problem."
Chelsea were quick to play down any suggestion of a conflict of interest for Abramovich on Thursday following the draw.
Simon Greenberg, the London club's director of communications, said: "Mr Abramovich is the owner of Chelsea and Sibneft, a company in which he is one of many shareholders, has a shirt sponsorship deal with CSKA Moscow.
"Mr Abramovich has no equity stake nor any direct interest in CSKA Moscow."
Greenberg added that Abramovich had no say in how sponsorship money was spent at CSKA.
CSKA president Yevgeny Giner has spent millions establishing them as the top team in Russia, breaking the league transfer record twice last year in signing Czech midfielder Jiri Jarosik from Sparta Prague for $3.7 million and then Croatian striker Ivica Olic from Dinamo Zagreb for $5.73 million.
This year CSKA have bought Russian internationals Sergei Ignashevich and Yevgeny Aldonin and Brazilian Under-23 striker Daniel Carvalho.
Abramovich watched two CSKA matches in the VIP box with Giner last season and also saw them play Rangers in Glasgow this week.
CSKA are fourth in the Russian League after 20 matches, three points behind the leaders, while Chelsea have won all three of their opening matches in the English Premier League.
CSKA begin their Champions League campaign at European champions Porto on September 14, while Chelsea are at Paris St Germain in their opening Group H match on the same night.
Chelsea meet CSKA in London on October 20 and in Moscow on November 2.