Niko Kovac jumped to the defence of the struggling Serhou Guirassy, insisting "the ball just won't go in" for the Borussia Dortmund forward.

Guirassy top-scored for Dortmund with 21 Bundesliga goals last season, with his tally only bettered by Bayern Munich striker Harry Kane.

The Guinea international also made a strong start to this campaign with four goals in his side's opening three league games.

However, he has failed to find the net in each of his last five Bundesliga outings, but Dortmund boss Kovac is unconcerned by his striker's scoreless streak.

"I see that he's not scoring goals at the moment. But I also see that he's working hard," he told reporters ahead of Dortmund's DFB-Pokal clash with Eintracht Frankfurt on Tuesday.

"It sometimes happens in a striker's career that the ball just won't go in. I'm backing him, he is and remains a very, very important player."

Dortmund last won the DFB-Pokal in 2021, but have failed to progress beyond the quarter-finals since, suffering a second-round exit at the hands of Wolfsburg in last season's competition.

Kovac, though, knows his side face a tough test against free-scoring Frankfurt, who have netted 21 times in the Bundesliga this term, with only Bayern (30) doing so more often.

"We are aware that the cup has gained in importance in recent years," Kovac added. "We know how difficult it is, but we have shown in recent games that we have what it takes.

"[Frankfurt have] scored a lot of goals, but they've also conceded quite a few [18 in Bundesliga]. They have a lot of potential, they're young and talented. We have to play our game from the first to the 90th, or even the 120th minute."