Stevens heads to Gelsenkirchen for the first time since he was sacked by Schalke last December, after an ill-fated 15-month spell with the German club, with PAOK looking for a good start to their UEFA Champions League two-legged qualifying play-off on Wednesday.
It was the 59-year-old's second stint at the Veltins Arena, following a six-year tenure from 1996-2002 where he led the club to the UEFA Cup and two German Cup crowns.
"Well, of course, you're happy when you come back after a short time to play Schalke as an opponent, because I get to see a lot of friends and people I worked with again; people who I worked with successfully," Stevens said on Tuesday.
"But I have to say this very clearly; we really are the outsiders and that we are here, we didn't think it was possible either but we are here and we will give it our best.
"I think that Schalke have also acquired some good replacements for certain positions.
"So therefore if you compare that with PAOK, we can't buy any players for €8million. We just don't have that possibility. We have a totally different budget."
"Yes, you have said it rightly, Huub was one of the club's greatest managers. I think that the team and also the club and the fans are looking forward to seeing him," Schalke defender Benedikt Howedes said.
"But a fact is also that (Wednesday) it's not a match between Schalke 04 and Huub Stevens but between Schalke 04 and PAOK Saloniki."
"We expect them (PAOK Salonika) to be a really strong team," Keller said.
"We have watched their opening league game in Greece, but we have also watched both of their UEFA Champions League qualifying games (versus Metalist).
"I will show some scenes from their games to the team tonight. It's a very good team. They were not inferior to Metalist."
