Sion's appeal against their expulsion from the tournament will be heard by UEFA's appeals body this morning but the Swiss club are also pursuing several civil court cases against the initial judgment.

Celtic are preparing for a game against Atletico Madrid in Spain but Sion have also booked a flight to the Spanish capital and controversial president Christian Constantin yesterday pledged to turn up as they fight the ruling on several fronts.

Constantin has consistently stated that his club could be reinstated at a later stage, even between the UEFA appeal and Thursday's kick-off.

Sion beat Celtic 3-1 on aggregate in the play-offs but were expelled for fielding ineligible players. The club signed six players when FIFA stated they were in the midst of a transfer embargo, but Sion have a different interpretation of the length of the ban.

Despite the ongoing saga, Celtic captain Scott Brown insists his team will be fully focused for the opener against Atletico.

Brown said: "Once we figure out if we're in or not, we'll take it from there.

"It's going to be a big game for us, especially going over there for our first game.

"We will take it as it comes and, if we get into it, it's perfect for us.

"Whatever happens happens, but we are going to take it as one of the biggest games of our season so far.

"The last couple of years we have not been in Europe, so that's been disappointing for the club, especially for the players.

"But I think the players around the squad now are probably the best I've been involved with. I'm sure we will give it everything we've got."

Brown is nursing an ankle injury that has forced him to miss Saturday's 4-0 SPL victory over Motherwell, and is hoping to make the Vicente Calderon clash.

"I'm getting very close to being fit," Brown said. "I'm touch and go for Thursday but I'll be fine for Sunday.

"I did it in the Scotland game (against Denmark) a few weeks ago and I've been playing with a tender ankle for the last couple of weeks and it has maybe just got the better of me the last few days.

"I'm desperate to get back in on Thursday. I will try training tomorrow or Wednesday and take it from there."