UEFA also reiterated that the case should be settled at the Court of Arbitration for Sport (CAS), not in a civil court.
The Swiss club, kicked out of the competition for fielding ineligible players and replaced by Celtic, said last week that a civil court in Vaud canton, where UEFA headquarters is based, had ruled that it should be reinstated.
But UEFA said it could not reverse a decision made by its independent disciplinary body.
"The UEFA Executive Committee unanimously stated that it had no statutory authority to reinstate FC Sion," said the statement.
"This [is] the sole prerogative of the disciplinary instances of UEFA, which operate under the statutes in an independent manner with no influence whatsoever from the UEFA administration or UEFA Executive Committee.
"As the UEFA disciplinary bodies have twice ruled on this case, the UEFA executive committee unanimously decided to await the Court of Arbitration for Sport (CAS) decision on the merits of the case.
"UEFA wishes to state strongly that, of course, it respects the law and that national law itself recognises the competence of the disciplinary structures that are specific to sport.
"This includes the role of the CAS in Lausanne, whose independence has been recognized by the Tribunal Federal of Switzerland. In this specific case, UEFA is constitutionally unable to apply to the letter of the super provisional and provisional measures decided by the civil court."
UEFA added that last week's civil court ruling was effectively an injunction valid for 60 days and that Sion would have to ask for a full legal hearing if they wanted to make it permanent.
"UEFA noted that the Tribunal Cantonal de Vaud also recognizes the role of the CAS as the competent entity able to decide on the merits of such a case, and gave FC Sion 60 days to initiate proceedings to do so," said UEFA.
UEFA added that Sion had signed an agreement recognising UEFA and CAS as the sole authorities for decisions on sporting matters.
Sion signed six new players in the summer despite being subject to a transfer ban imposed by FIFA after being found guilty of inducing an Egyptian player to break his contract with his previous club to join them in 2008.
Sion then fielded some of the players in a Europa League qualifier against Celtic which they won 3-1 on aggregate.
