Novak Djokovic's chances at the upcoming US Open 2025 appear to be in jeopardy after a new video showed the Serb getting physical treatment for a knee injury during a practice session ahead of the tournament.The Serb has had a below par 2025 by his own standards, and is yet to win a tournament this year. At Grand Slams, he exited the Australian Open, the French Open and Wimbledon all in the semifinals stage.Now, with the US Open coming up, the former World No. 1 will be looking for his 25th Grand Slam title, which would make him the player with the most Majors in tennis history and above Margaret Court. Unfortunately, that now appears to have hit a wall.In a video that has surfaced on social media recently, Djokovic can be spotted with a trainer giving him treatment on his right knee during one of his practice sessions in Montenegro. It appears to be the same knee issue that has continued to affect the 24-time Grand Slam champion in recent months, leading to a long line of withdrawals.In fact, Djokovic has not played a single match since Wimbledon, and was likely to show up at the US Open without any warm-up on the hardcourts following the end of the grass swing. At the moment, his team has not announced any news about his fitness, and it remains to be seen how he will arrive at New York at the end of the month.Novak Djokovic is a four-time winner at the US OpenUS Open Tennis Championship 2023 - Source: GettyNovak Djokovic, should he come to New York, will arrive as a four-time US Open champion, having won the tournament before in 2011, 2015, 2018 and 2023. The 2023 title remains his most recent Grand Slam trophy till date.This year, the defending champion is World No. 1 Jannik Sinner. The Italian beat Djokovic at the French Open and Wimbledon this year, going on to finish as the runner-up at the former and winning the latter. Last year, he took on Taylor Fritz in the final and beat the American in straight sets.At the US Open, Sinner will be among the top favorites to win the title again, followed by World No. 2 Carlos Alcaraz. Alcaraz, who won at Flushing Meadows in 2022, is on a hot-streak at the moment, having reached the final of the Cincinnati Open after winning the French Open and finishing runner-up at Wimbledon.