Florian Wirtz will be sidelined 'for months' after tearing knee ligaments as Bayer Leverkusen lost 1-0 at home to Cologne Sunday while elsewhere in the Bundesliga, Erling Haaland made his long-awaited return from injury for Dortmund.

Wirtz, 18, tore the anterior cruciate ligament in his left knee during a first-half challenge in Leverkusen's derby defeat.

He was stretchered off in clear distress.

The attacking midfielder "will be out for several months", Leverkusen said in a statement after giving the diagnosis.

He misses Germany's friendlies against Israel and the Netherlands later this month, facing a race against time to be fit for the World Cup in Qatar which kicks off in November.

Wirtz's injury capped a bad day for Leverkusen as Cologne's Kingsley Schindler came off the bench to volley in a superb second-half winner for his first Bundesliga goal.

The loss of Wirtz is a serious blow to Leverkusen with their top-scoring Czech striker Patrik Schick already sidelined by a torn calf.

Leverkusen are third in Germany's top flight, but suffered a second defeat in three days after losing to Atalanta in their Europa League last 16, first-leg tie on Thursday.

Cologne are seventh in the table as Steffen Baumgart's visitors out-thought and out-muscled Leverkusen.

The hosts lost three players in the first half of a bruising derby as defenders Jeremie Frimpong and Odilon Kossounou also suffered leg injuries.

Later, Haaland made his first appearance since late January as Dortmund closed the gap behind Bundesliga leaders Bayern Munich with a 1-0 home win over Covid-hit Arminia Bielefeld.

Haaland came on for the last half hour at Signal Iduna Park after Marius Wolf's first-half winner against strugglers Bielefeld who had six players and head coach Frank Kramer out with Covid.

Dortmund were also missing defenders Mats Hummels and Raphael Guerreiro who also tested positive for the coronavirus last week.

The home win allowed Dortmund to trim Bayern's lead in the table to seven points after the league leaders were held to a 1-1 draw at Hoffenheim on Saturday.

Dortmund can reduce the deficit further on Wednesday when they host Mainz.

There was more good news for Dortmund as teenage US international Giovanni Reyna also made his return from injury with a brief cameo.

Japan midfielder Daichi Kamada scored the winner as mid-table Eintracht Frankfurt came from behind to seal a 2-1 win at home to Bochum.