Celtic take on Athletico Madrid on Wednesday in what is a must win game, according to boss Neil Lennon.
Celtic sit third in a tightly contested group, but a win will see them leap frog their top-of-the-league opponents.
“It's a huge game for us because they are a class side,” said Lennon
“They won this tournament not so long ago and they have a team full of quality players. We need to win it to stand a chance of qualifying.”
Championship side Birmingham will have a tough test against Braga, who can confirm their knockout place with a win in Portugal on Wednesday.
Birmingham, Braga and Club Brugge are all level on seven points in Group H going into the pivotal round of fixtures.
“Of course we know that Braga are a very good side with European pedigree and that they also have an impressive home record over the years, so I think this is going to be our sternest test,” said Birmingham boss Chris Hughton.
Fulham travel to Group K leaders FC Twente on Thursday knowing a win will send them through to the knock out stages.
The sides drew 1-1 at Craven Cottage in September, and Fulham striker Bryan Ruiz has given his team information as well as players to watch from his former side.
The striker said: "I think we can win the game but we have to be really focused, defend well and also keep the ball when we have it.
"We have to take care of Nacer Chadli, Luuk De Jong and Ola John and also Emir Bajrami - if those players play they are very good,” added Ruiz.
Stoke sit top of Group E and will only need a draw at the Britannia on Thursday against Dynamo Kiev to ensure progression to the knock-out stages.
The Potters are yet to lose in their last six home European ties and have not lost in their last 10 European games home or away.
"I looked at it as a group that was extremely difficult and Thursday is a cup final for us,” said Stoke manager Tony Pulis.
Meanwhile Tottenham take on Group A leaders PAOK at White heart Lane on Wednesday looking to gain a vital three points.
Harry Redknapp will continue to rotate his side against the Greek high-flyers although he knows the importance of the game.
“It's a must-win game as we're a point behind and you can see Rubin beating Shamrock," said the 64-year-old.
"I would have made 11 changes from Saturday but Roman Pavlyuchenko tweaked his knee yesterday so he is struggling and Giovani dos Santos has a groin strain,” added the Spurs boss.
A win for Tottenham will leave them on ten points which would see them top the group providing Rubin do not win at Shamrock Rovers