Defending champions Bayern Munich are waiting to see if Dutch winger Arjen Robben recovers from a heavy cold in time to face Bundesliga strugglers Cologne on Saturday.
Robben has been in stellar form for Bayern recently, despite missing the first half of the season with a thigh injury and has scored three goals in four games, incluidng two in the German league.
The 26-year-old sat out training on Thursday and a decision on whether he plays in Cologne will only be made closer to kick-off with Turkey midfielder Hamit Altintop on stand-by to deputise for the World Cup runner-up.
Cologne are third from bottom and locked in the battle to avoid relegation, but a rare win over Brmen two weeks ago shows they will not be easy to beat.
There is some good news for Bayern with French midfielder Franck Ribery expected to be on the bench after an impressive display in Thursday's training nearly three weeks out with an ankle injury.
The 27-year-old sprained his knee in the first post-Christmas fixture away to Wolfsburg three weeks ago, and has not played since then, but he resumed training last Sunday and could feature as a sub in Cologne.
Bundesliga leaders Dortmund are 11 points clear at the head of the table with Leverkusen second and Bayern third, 14 points adrift of the top team, so Munich cannot afford to leave Cologne without three points.
Louis van Gaal's men have won seven of their last eight games and only a draw at Wolfsburg has blemished their perfect record so far in 2011.
"We slipped up in Wolfsburg, but we've otherwise made a good start to the second half of the season," said midfielder Andreas Ottl.
But Bayern need to improve on their recent record against the men from Cologne: Munich have not beaten them in four matches over the last two-and-a-half years.
Second-placed Leverkusen are at mid-table Nuremberg on Saturday with Germany captain Michael Ballack set to make his second start after a leg injury kept him out since last September.
Hoffenheim, eighth in the league, take on mid-table Kaiserslautern with coach Marco Pezzaiuoli having signed a contract on Thursday which will keep him at the Bundesliga side until 2014.
Pezzaiuoli, 42, took over as head coach last month after stalwart Ralf Rangnick quit in early January after four-and-a-half years in charge.
Since taking over as head coach, Pezzaiuoli has endured a torrid time as his team were dumped out of the German Cup by second division Energie Cottbus and went three games without a win before they won 1-0 at Schalke last weekend.
Borussia Dortmund v Schalke 04
Mainz 05 v Werder Bremen
Hoffenheim v Kaiserslautern
Cologne v Bayern Munich
Hanover 96 v VfL Wolfsburg
Nuremberg v Bayer Leverkusen
Borussia M'gladbach v VfB Stuttgart
Hamburg v St. Pauli
Freiburg v Eintracht Frankfurt