Skipper Scott Brown believes Salzburg are not only the toughest team Celtic have faced this season but also the fittest.
A win over the already-qualified Austrian side in their Europa League Group D clash at Parkhead tonight will see Ronny Deila's side also book their place in the last 32 of the competition with one game remaining, as will a draw or defeat if Dinamo Zagreb fail to win at Astra.
However, Brown was impressed by Salzburg in the section opener in September when the home side battled back after going behind twice to the Hoops - with the Scotland captain scoring the second - to grab a merited 2-2 draw.
Salzburg won their next three fixtures to take them on to 10 points, two clear of Celtic, although Brown, who returns after missing the 2-1 home Premiership win over Dundee on Saturday though suspension, does not think that will affect the visitors' attitude.
"I don't think it's going to matter to them that they have qualified because they are a great team," he said, before being asked if asked if he felt Adolf Hutter's side are the toughest Celtic have faced this season.
"Yeah, definitely, I think they are the fittest as well," he said.
"You see their right-back pressing Emilio Izaguirre high up the park to put him under pressure, it shows their will to win. It was a hard game when we played them over there but we managed to get a point and I think it shows you how well we're doing in this competition.
"To finish top of the group would be huge but the main thing is to qualify and if we qualify then we've done really well because it is a hard group.
"If it goes down to the last game (away to Dinamo) so be it but hopefully we can do it at home. It would be great to do it in front of our own fans as well."
Celtic boss Ronny Deila, meanwhile, believes the rigours of the Scottish Premiership stands his men side in good stead for the tie.
"There have been a lot of big games this season but this is important because if we win we go top of the group and go through," said Deila, who must once again contend without ineligible striker John Guidetti.
"It is a good game as well. We are going to meet a very good opponent and we will be tested at the highest level.
"They are very different from a lot of the other teams we have met.
"They are very aggressive, intense with their pressure and direct in their play.
"We have to cope with that but we are quite used to that in the Scottish league, it is also a direct league with intensity.
"So it is a game that will suit us and we saw that when we played them away we can handle it.
"If we win the game we are in the position we want to be so we are really up for the game."
Deila believes Salzburg are a match for any team they have played in Europe this season, including Legia Warsaw who knocked Celtic out of the Champions League qualifiers before the Hoops were reinstated due to an administration error made by the Polish club.
However, he does not believe opposite number Hutter will change his side's approach to the match just because they already through to the competition's knock-out stages.
He said: "I think they are the best. Maybe Legia Warsaw, it is very hard to say, we have met good opponents in Europe but Salzburg have had some good results and been at a high level for a couple of years.
"But I don't think they will approach it any differently. It is clear to us what we are going to meet so we just have to be up for it."
CELTIC winger Aleksandar Tonev's appeal over his seven-game racism ban is to be heard on Thursday, December 4.
The 24-year-old Bulgarian, on loan from Aston Villa, was found guilty by the Scottish Football Association's disciplinary tribunal of "offensive, insulting and abusive language of a racist nature" towards Aberdeen defender Shay Logan in a league match in September.