Aug 18 (Reuters) - Austria"s Dominic Thiem will not defend his U.S. Open title after having to pull out of the hardcourt major with a wrist injury, the world number six said on Wednesday. Thiem, who suffered the injury in June at the Mallorca Open and was also forced to skip the grasscourt major at Wimbledon, said on Twitter that he will miss the rest of the 2021 season. "The past six months, I"ve been following the medical advice, wearing the wrist splint, doing exercise to stay in shape... but then last week I hit a ball during training and started to feel some pain again," said the 27-year-old. "After some tests, they (the doctors) said my wrist needs more time, so we"ve all agreed on being conservative and to give my wrist some time to recover... It has been a tough decision but I know this is what I have to do." This is the second straight year that the defending champion at Flushing Meadows has withdrawn from the event after Rafa Nadal skipped the 2020 edition due to concerns over the coronavirus. The U.S. Open runs from Aug. 30 to Sept. 12. Reporting by Sudipto Ganguly and Dhruv Munjal; Editing by Andrew Cawthorne and Hugh Lawson Our Standards: The Thomson Reuters Trust Principles.