The Germany international was forced to pull out of the national team for their games against Austria and Poland over the last week and he may also miss the match at the Borussia Park stadium.
He is currently training alone in a bid to be fit and his Swiss coach Favre hopes he will recover.
"Of course Marco is a very important player for us," he said. "He is a player who can make the difference.
"If he is injured, though, we can do nothing about that other than find another solution.
"We have plenty of alternatives in the squad with Juan Arango, Lukas Rupp, Patrick Herrmann or Yuki Otsu all able to play on the wing.
"He (Reus) will take part in our final training session and afterwards we will decide whether he can play."
Otherwise, the two-week break for international matches has been beneficial to other members of Favre's squad.
Those players who were away with their nations have returned without any injuries while Martin Stranzl and Marc-Andreter Stegen have used the time to recover.
And Favre is looking forward to having a 12th man with the stadium set to be a sell-out.
"It is great that so many fans will be coming," he said.
"I am glad that the fans are happy and we have got to keep performing well and give everything in every game to ensure it remains that way."
Kaiserslautern will be aiming to make amends for their 3-0 defeat to Bayern Munich a fortnight ago.
"We need to become more compact and more dominant in our tackling," said their coach Marco Kurz.
"But the team has improved a great deal in this respect in the last two weeks.
"This intensive period of training will be reflected in the coming matches. It is crucial that we play better."