The Bundesliga side go into their final Group G encounter knowing that a win, coupled with a Sporting defeat against leaders Chelsea, will see them into the knockout stage.
Slovenian outfit Maribor are out of the running to progress from the pool but will gain a Europa League spot with victory at the Ljudski vrt.
Former Chelsea boss Di Matteo has enjoyed a relatively fruitful start to life at the Veltins-Arena, winning six of his opening 10 games in all competitions, although his fledgling reign could be dealt its first major blow with an exit on Wednesday.
Since their 5-0 drubbing at the hands of Chelsea last time out in the Champions League, Schalke have put eight past Mainz and Stuttgart.
Di Matteo will be hopeful his side can continue their prolific streak and usurp Sporting in second, with the Italian buoyed by what he has seen since arriving at Schalke.
"Right now, I'm not worried," he told Kicker.
"We'll see after the game what the situation will be and then I can comment on it.
"It is impossible to realise everything very quickly and to achieve continuity is very difficult. It's all about good, hard training and ... in this regard, I have at Schalke found a very high willingness from the players here.
"That is why I remain optimistic."
Di Matteo has doubts over the likes of Sidney Sam (thigh) and Kevin Prince-Boateng (ankle), while opposite number Ante Simundza could be without Petar Stojanovic (nose).
However, experienced defender Ales Mejac made his return from a hamstring injury in Saturday's 4-1 win over Radomlje.
Ljudski vrt has proven something of a fortress for Maribor in Europe this term, having won two and drawn one of their three home games in qualifying before taking points off Sporting and Chelsea in Slovenia.
Mejac feels the home crowd will play their part in making life difficult for Schalke on what will be a pivotal evening in both sides' seasons.
"Who would have thought that we would, in the last round, still have opportunities to progress," he told Maribor's official website.
"Many people are surprised but our honest performances have got us to this point and we already cannot wait for Wednesday.
"We are playing at home in front of a full stadium and our fans will once again be our 12th player. All things are possible."
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