In nearly any other year, Danka Kovinic would seem like a dream opponent for Serena Williams.
Kovinic, 27, from Montenegro, is the 80th-ranked player in the world and has never been ranked higher than 46th. She has never made it past the third round of a Grand Slam tournament and has never made it past the second round at the U.S. Open.
Clay is probably her best surface, rather than the hardcourts of the U.S. Open. She has not won a singles match since the French Open in May, making her winless this summer.
So why does she seem like a problematic matchup for Williams, a 23-time Grand Slam champion?