Russia’s Maria Sharapova has pulled out of this weekend’s Fed Cup semi-final against the United States.

The world No.2, who has yet to make her debut in the team competition, made the announcement on Monday on her official website.

The Russian star has a shoulder injury and has been told by doctors to rest for 10 days.

Sharapova has been struggling with the injury for much of the season, including during her 6-1 6-3 loss to eventual champion Venus Williams in the fourth round at Wimbledon last week.

“All the scans and tests show improvement in my shoulder but I still have a tremendous amount of swelling in the area,” Sharapova said on www.mariasharapova.com.

“Since having another cortisone shot in 2007 is not an option for me, I need to monitor my shoulder at all times.

“The good news is that Russia still has an amazing team, and I believe they will still have a very good chance to win the match.”

Elena Vesnina, ranked 58th in the world, replaces Sharapova in the squad, and further changes may be on tap.