Borussia Dortmund coach Jurgen Klopp will re-shuffle his midfield when the German league leaders travel to Hertha Berlin on Saturday after losing Japan winger Shinji Kagawa through injury. After scoring four goals in his last four matches, Kagawa rolled an ankle in training on Thursday and is expected to be out for at least the next fortnight. Klopp is already without Germany\'s teenage midfield star Mario Goetze for the next few weeks with a groin injury. He has plenty of options as Poland striker Robert Lewandowski can drop back into the attacking midfield role to allow Paraguay striker Lucas Barrios to start or ex-Germany Under-21 product Ilkay Gundogan can come into the midfield. \"I can\'t even tell you how we will change the team around. I\'m still thinking,\" said Klopp. Dortmund have won all three of their league games since the start of the year and are two points ahead of Bayern Munich in the table. The game will sell-out Berlin\'s Olympic Stadium and some 18,000 Dortmund fans are expected to make the trek across north Germany. While Dortmund concern themselves with the loss of Kagawa, Hertha have suffered five straight defeats and sacked coach Michael Skibbe last Sunday in the wake of their 5-0 defeat at Stuttgart. Ex-Hertha midfielder Rene Tretschok has been appointed the interim coach as they look for only their fifth league win all season with the team hovering above the relegation zone. Bayern on the road Second-placed Bayern Munich, who are two points behind Dortmund, are at bottom side Freiburg on Saturday, but they have injury worries of their own after Bastian Schweinsteiger\'s ankle injury. Austrian teenager David Alaba took Schweinsteiger\'s place and partnered Luiz Gustavo in the defensive midfield role in last weekend\'s 2-0 win over Kaiserslautern and earned the praise of coach Jupp Heynckes. \"David has fitted in superbly. He\'s done a magnificent job,\" enthused the Bayern boss, but his team failed to impress against a weak team as goals by Germany\'s Mario Gomez and Thomas Mueller saw them through. With the UEFA Champions League trip to face Manchester United-slayers FC Basel in the Round of 16 first leg on Wednesday, Bayern badly need a good performance at Freiburg. Third-placed Borussia Moenchengladbach are waiting on the fitness of star midfielder Marco Reus for their match against Kaiserslautern on Saturday after the 22-year-old suffered a groin injury in training. Gladbach are this season\'s dark horses having already beaten Bayern both home and away and are only three points behind Dortmund having just avoided relegation last season by winning the end of season play-off. With 13 goals in 19 games, Reus, who joins Dortmund this summer, has been their shining star and many of their attacks at least start or finish with him playing a key role. Midtable Hamburg look to continue their renaissance under ex-Bayern midfielder Thorsten Fink in the north German derby when they host Werder Bremen. Hamburg have lost just once in 12 league games since he took charge in October, but Fink\'s team has its work cut out as Bremen welcome back from suspension striker Claudio Pizarro, who has scored 15 league goals this season.