Both Schalke and Bayern are into the last 16 of the Champions League, but while Munich are up to fifth in the table after last Saturday's 4-1 win over Eintracht Frankfurt, Schalke crashed 5-0 at Kaiserslautern and are 15th.
"Schalke are a tough opponent," said Tymoshchuk, the Ukraine captain, who scored twice against Frankfurt for Bayern.
"The league table is not a fair indicator.
"Schalke are in a difficult situation, especially following the defeat at Kaiserlautern. They will be dangerous."
Schalke are in something of a crisis.
Despite reaching the knock-out stages of the Champions League they are erratic and coach Felix Magath demoted US midfielder Jermaine Jones to the reserves in midweek after a poor performance.
Magath was called in for a crisis meeting on Wednesday and Schalke's bosses have backed him to get the club out of the current predicament.
Reports have been denied that the Royal Blues have a Plan B if the side keeps losing with ex-Tottenham Hotspur and Stuttgart coach Christian Gross lined up as a possible replacement for Magath.
Schalke look set to welcome back Germany defender Christian Pander after 17 months out with a knee injury, but while they struggle, Bayern continue to rise.
Tymoshchuk has taken over at the heart of Bayern's midfield alongside Bastian Schweinsteiger with captain Mark van Bommel out injured and was instrumental in the win over Frankfurt.
France midfielder Franck Ribery played his first full 90 minutes against Frankfurt since injuring his ankle in September and he admits both sides will be desperate for three points.
"This will be a difficult game, they will go with a lot of passion into the game because they really need the three points, just like us," he said with Bayern 14 points behind leaders Dortmund.
With wintry weather sweeping Germany, the temperature is expected to stay well below zero degrees for Saturday's game, although the extreme cold will be no problem for former Zenit St Petersburg star Tymoshchuk.
With Dortmund defeating Karpaty Lviv 3-0 in the Europa League on Thursday, the leaders will play at Nuremberg on Sunday night.
Jurgen Klopp-coached Dortmund have a seven-point lead and second-placed Mainz have a local derby at Frankfurt on Saturday.
They will be without central defender Bo Svensson, who has a knee injury.
"We must go back to playing to the limits," said Mainz coach Michael Tuchel, whose side have won their last two league games to break a three-match losing streak.
VfB Stuttgart v Hoffenheim
VfL Wolfsburg v Werder Bremen
Eintracht Frankfurt v Mainz 05
Borussia M'gladbach v Hanover 96
Freiburg v Hamburg
Schalke 04 v Bayern Munich
Bayer Leverkusen v Cologne
Nuremberg v Borussia Dortmund