BERLIN, May 7 (Xinhua) -- Borussia Dortmund defender Niklas Sule has announced that he will retire from professional football at the end of the season, saying a frightening knee injury against Hoffenheim turned a long-held thought into a final decision.

The 30-year-old former Germany defender said on the "Spielmacher" podcast that his Dortmund contract expires on June 30. Sule explained that the idea of stepping away from the game had been on his mind for some time, but the decisive moment came after Dortmund's match at his former club Hoffenheim in mid-April, when he injured his knee.

The center-back said an examination in the dressing room left him fearing the worst after the club doctor and physiotherapist checked the joint. "I went into the shower and cried for 10 minutes," Sule said, recalling the moment after the tests. He added that he believed at the time: "It is torn."

An MRI scan the following day brought relief because the injury was not a cruciate ligament rupture. But Sule said the scare also clarified his future. "It was one thousand percent clear to me that it was over," he said.

Sule said the thought of having to deal with a third cruciate ligament injury, just as he was looking forward to independence, holidays and time with his children after football, was something he could not face.

Sule joined Dortmund from Bayern Munich in the summer of 2022 and has since made 109 appearances for the club, scoring three goals. He has played 299 Bundesliga matches and won 49 caps for Germany.

His first season at Dortmund ended in painful disappointment as the club narrowly missed out on the Bundesliga title. Sule said the buildup to the final game against Mainz had stayed with him because of the intensity he felt in the hotel, on the way to the stadium and before kickoff. "That was one of the craziest moments before the Mainz game," Sule said.

Dortmund also reached the Champions League final in Sule's second season. Looking back on his time at the club, he highlighted the dressing room, the 80,000-capacity stadium and the welcome he received from Dortmund supporters. "I was always openly received by the fans," he said, adding that he would miss the city and the club environment. ■