With a busy schedule ahead of her Calendar Slam attempt at the US Open, Serena Williams has withdrawn from the Bastad clay event.

The American, who claimed the 21st Grand Slam title of her career when she beat Garbine Muguruza in Saturday’s Wimbledon final, made the decision shortly before she was due to face Klara Koukalova in the second round.

Newly-crowned Wimbledon champion and top seed Serena Williams only arrived in Bastad on Monday following her weekend exploits and will play Belgian qualifier Ysaline Bonaventure on Wednesday.

“I was having some pain in my elbow”, the World No. 1 told reporters at a press conference. I have such a great time. “I’m going to take some time off, I’m going to get some treatment, and I’m going to continue to do things for it. I’ll do what’s best for my body and continue from there. My fans here are really unbelievable, I love all you guys”, she said to resounding applause.

Williams offered no details of the injury, which was incurred during practice Thursday.