Defender Juninho was forced out of Tuesday night’s 3-0 loss to PSV prior to the match after Fifa ruled the eight-match suspension he picked up in Brazil was still valid following his summer transfer to the Danish side.
The 26-year-old received the ban over his part in a brawl between Bahia and Ceará which saw six players punished with a total of 54 matches.
He served two of those in Brazil before his move to Midtjylland from his parent club Palmeiras. He then featured at centre-back in the 2-1 second-leg victory over Celtic. Juninho also squared off against Viborg in the Danish top flight.
Midtjylland were told to sit the player prior to their trip to Rotterdam on Tuesday, prompting questions over whether they could be forced to forfeit the tie for fielding an ineligible player in a similar scenario that saw Celtic reinstated into European competition following defeats to Sion in 2011 and Legia Warsaw in 2014.
However, Uefa have confirmed that Juninho's ban applies from August 2 onwards, meaning the Danes did not breach any rules by playing him against Celtic last week.
A Uefa spokesperson told the Scottish Sun: "With regard to your inquiry, we would, first of all, like to inform you that in accordance with Article 66 of the Fifa Disciplinary Code (2019 edition), any decision related to the extension of sanctions to have worldwide effect falls under the exclusive jurisdiction of the competent Fifa disciplinary bodies.
"We can confirm that Uefa was made aware by Fifa on 2 August of its decision taken on the same day regarding this case, i.e. after the Uefa Champions League second qualifying round tie between FC Midtjylland and Celtic FC."
Midtjylland sporting director Svend Graversen also insisted his club did nothing wrong.
He said: "Of course he was eligible.
"It has been confirmed that it will apply from now on and for the next six matches.
"We have known about it. This is not a surprise to us.
"We are sorry about the outcome and that it comes at this time. We have to look into that and see if we can appeal this decision."