Sion were excluded from the tournament on September 2 for fielding ineligible players, with Celtic promoted to the competition in their place.
UEFA are currently hearing the Swiss club's appeal against their expulsion ahead of Thursday's opening group game against Atletico Madrid.
A statement on Sion's official website read: "The civil court has this morning [Tuesday] ordered UEFA to admit FC Sion as a participant in the 2011-12 Europa League and to take all the measures necessary to include them in Group I of the UEFA Europa League for which FC Sion have qualified.
"The Canton de Vaud Tribune also orders UEFA to consider the players Stefan Glarner, Billy Ketkeophomphone, Mario Mutsch, Pascal Feindouno, Jose Goncalves and Gabri as eligible as FC Sion players and to admit them in the 2011-12 UEFA Europa League.
"The order has been declared immediately binding."
Sion beat Celtic 3-1 on aggregate in the play-offs but were expelled for fielding ineligible players after signing six players when FIFA stated they were in the midst of a transfer embargo.
Celtic are now preparing for a game in Spain but Sion's controversial president Christian Constantin claims his side also intend to travel to the Spanish capital.
UEFA have declined to make any comment until a decision is reached in Tuesday's appeal hearing.