In the midst of one of his best season, Alexandr Dolgpolov will be sidelined for the upcoming North American hardcourt swing due to a knee injury he suffered earlier this week during Hamburg where he lost in the third round to Tobias Kamke in three sets.

“I am really unhappy to announce that I injured my knee in Hamburg and I will probably need a surgery and will be out for 4-6 weeks,” he wrote on Instagram. “Disappointing,specially not playing the great event in Umag, the Us series and Davis cup play offs:((( hopefully il be back ASAP. К”

Currently ranked No. 21, Dolgopolov reached the semifinals earlier this year at Indian Wells where he stunned Rafael Nadal.

The 25-year-old also lost to Grigor Dimitrov in five sets in the Wimbledon third round.

Dolgopolov joins Nicolas Almagro as seeds already out of the US Open.