Celtic assistant boss John Collins admits the Scottish champions could struggle to land their January transfer targets if they do not clinch a knock-out round slot.
The Hoops host Red Bull Salzburg tomorrow night with a place in the last-32 within reach.
A win over the Austrian champions or the failure of Group D rivals Dinamo Zagreb to beat Astra in Romania would be enough to see Ronny Deila's men through with a game to spare.
But the Norwegian's right-hand man Collins fears defeat this week, combined with a slip up against Dinamo in their final group clash in Croatia, will leave the Parkhead outfit in danger of missing out on the names at the top of their transfer wish list.
The former Hoops midfielder said: "It is vitally important that we qualify. If we are looking for players in January and next summer, they will want to play in Europe.
"Good players want to be involved in the Champions League and Europa League. They don't just want to play domestic football. So it is really important that we qualify.
"Is it our biggest selling point? Yeah, it's very difficult to get top players if you are not in Europe."
It has not been an easy start for Deila since the former Stromsgodset boss moved to Scotland.
The Hoops were knocked out of the Champions League before dropping down to Europe's second-tier competition.
But while Celtic's best displays under their new manager have come in the Europa League, assistant boss Collins warned it will be a long time before they can seriously rival the continent's big guns.
"We have got a long way to go (before we can be competing in the latter stages of Europe regularly)," said the man who once helped Monaco to the Champions League semi-finals. "There has been a lot of new players in and we are still building.
"We know our players now, though. We have had five months together but like any side, we will always look to strengthen."
"We are seeing improvements on the training pitch and as the weeks go by we are getting better. But there is still a long way to go."
And Collins knows his men will not get an easy ride on Thursday against a side who he reckons are amongst the hardest working in Europe.
He said: "Salzburg are a good team. They play some high tempo football and love to press. They are probably one of the best - if not the best - pressing team in Europe.
"They don't give you a second on the ball and are always looking to pass forward.
"It will be a new challenge for us. It's something we don't get in Scotland. Most teams sit off us here, so it is the exact opposite."
Collins was talking as Celtic attempted to promote ticket sales ahead of Thursday's match.
The Hoops have come nowhere near to selling out Celtic Park this season.
But the 60,000-seater stadium was packed out for the two recent Scotland clashes with the Republic of Ireland and England and Collins wants to see those scenes repeated when the Bhoys run out.
"We would love to see the same kind of big crowds that were at the stadium for the Scotland games back," said Collins. "When the place is full there is no stadium like it.
"But it is up to us to keep winning matches and putting on entertaining performances if we the crowds back."