Sion have vowed to fight UEFA all the way after they were booted out of the Europa League and replaced by Celtic.
UEFA yesterday upheld Celtic's appeal that the Swiss club had fielded five ineligible players and Neil Lennon's side now go into Group I alongside Atletico Madrid, Rennes and Udinese.
FIFA applied a two-window transfer ban on Sion signing players after the disputed arrival of Essam El-Hadary in 2008.
The Swiss FA applied the ban in the first three games of the championship but Sion got the ruling overturned in a Swiss court -- and Pascal Feindouno, one of six summer signings, scored twice in the 3-1 win over Celtic.
Sion president Christian Constantin has been fighting the transfer ban all summer long and has until 5pm on Monday to appeal the UEFA decision.
"We have not lost anything at all yet," he claimed. "We have been part of a truncated process today. That is typically the method of Uefa. But next week, we will go to seize civil justice to invalidate this judgment."
Celtic are now preparing themselves to face Atletico Madrid away from home on September 15, just three days before going to Ibrox to meet Rangers in the Scottish Premier League.
A Celtic statement said: "We have been advised by UEFA that the two protests relating to the matches against FC Sion have been upheld, as a result of which each match has been forfeited in favour of Celtic.
"We are pleased by this decision, the approach which has been taken by UEFA and the fact that UEFA rules and regulations have been upheld.
"We are also grateful for the support of the SFA in this matter."
Meanwhile, Rangers' tax troubles continued yesterday when it was found that Her Majesty's Revenue and Customs had frozen a bank account over an unpaid tax bill of £4.1m.