With the international break over and the Bundesliga back in action, defending champion Bayern Munich is looking over its shoulder at Wolfsburg.

Bayern leads the league after 11 matches and will next face Hoffenheim on Saturday, while Wolfsburg is enjoying an eight-game winning streak across all competitions ahead of its visit to Schalke.

At the other end of the table, Borussia Dortmund hopes it has turned things around after completing its worst start to the league. Dortmund next faces Paderborn on Saturday.

Also, the stakes will be high on Sunday in the northern derby between struggling rivals Hamburger SV and Werder Bremen.

Here are some things to know ahead of this weekend's matches:

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BAYERN BLOW

It's been a mixed week for Bayern.

The club was dealt a blow with captain Philip Lahm ruled out for up to three months after breaking his right ankle, while director of sport Matthias Sammer's contract was extended until 2018.

The club also confirmed former president Uli Hoeness will return in some form if he gains day parole from his 3 1/2-year prison term for tax evasion.

Lahm's loss is a big setback for coach Pep Guardiola, who previously described the versatile defender as the most intelligent player he has trained. Whether in midfield or at the back, Lahm could be relied upon to read the game, snuff out chances, complete his passes and lead the side with his calm demeanor.

Bayern was already missing Javi Martinez, David Alaba, Thiago Alcantara, Holger Badstuber, Claudio Pizarro and backup goalkeepers Tom Starke and Pepe Reina.

Bastian Schweinsteiger's return to training is a timely one, though Guardiola will be thinking of other alternatives for Saturday's visit of Hoffenheim.

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WOLFSBURG WINNING

Wolfsburg's 2-0 win over Hamburg was the club's sixth in a row in the Bundesliga, keeping the side four points off Bayern's pace.

Only Bayern has scored more goals, 27 compared to 22, while Wolfsburg's defense is the third best in the league.

Kevin de Bruyne is emerging as the side's key player. The Belgian has set up nine goals already - more than any other in the Bundesliga - while his commitment and workrate are helping in other ways, too.

The squad is in good shape ahead of Saturday's game at Schalke. Ricardo Rodriguez, Marcel Schaefer and Daniel Caligiuri have all shaken off knocks, while Christian Traesch's recovery from flu gives Dieter Hecking a full squad to choose from.

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SCHALKE STUTTERING

Former Chelsea coach Roberto di Matteo was supposed to turn Schalke's season around after taking over from Jens Keller. But there has been no discernible improvement under the Swiss-Italian, who has claimed six points from four Bundesliga games.

Schalke is mid-table, five points above last-place Stuttgart and 13 behind Bayern. So far, there hasn't been much evidence that the all-important Champions League qualification places are within reach.

"We have to start upping our performances now and being successful on a consistent basis," Schalke board chairman Clemens Toennies told Kicker magazine. "Then we can still achieve our aims."

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DORTMUND DESPERATE

Dortmund needs another win against promoted Paderborn on Saturday to get away from the relegation zone.

The 2011 and 2012 champions were in last place before their deserved but somewhat fortuitous 1-0 victory over previously unbeaten Borussia Moenchengladbach.

While injuries have played their part, defensive lapses and a lack of efficiency up front have cost Dortmund dearly, underlining the importance of departed striker Robert Lewandowski.

Dortmund coach Juergen Klopp hopes Marco Reus will have recovered from the ankle injury he sustained against 'Gladbach, while both Jakub Blaszczykowski and Nuri Sahin played in a practice match on Tuesday as they make their ways back from serious knee injuries.

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NORTHERN NERVES

Traditional rivals Hamburg and Bremen have clashed more often than any other sides in the Bundesliga. Sunday's derby in Hamburg will be the 101st league meeting and 146th overall, with Bremen boasting 55 victories to Hamburg's 50.

But their glory days seem a long time ago. It's been 10 years since Bremen won the double, while Hamburg's last league title was 31 years ago.

Both sides are fighting relegation this season after firing their coaches. Bremen has momentum under new coach Viktor Skripnik with two wins from two games, while Hamburg is a point behind with the worst attack in the league (four goals scored in 11 games).