Serbia have lost their appeal against UEFA's decision to admit Kosovo to its ranks, the Court of Arbitration for Sport (CAS) said on Tuesday.
The Football Association of Serbia (FAS) had argued that UEFA breached its own rules by allowing the Football Federation of Kosovo (FFK) full member status at its Congress in May 2016.
Serbia has refused to recognise Kosovo as a state since the Balkan republic's declaration of independence in 2008.
But CAS ruled that although UEFA's statutes were ambiguous, Kosovo was recognised by the majority of United Nations member states as being an "independent state" and was therefore entitled to admittance.
Kosovo played their first competitive match against Croatia in a World Cup qualifier in October. Croatia won 6-0.