British number one Johanna Konta has pulled out of the US Open, just hours before she was set to play her opening match on Monday.

The reason for world number 47 Konta's late withdrawal was unclear.

Konta, who missed Wimbledon because of a close coronavirus contact and then the Olympic Games after contracting it herself - has been managing a long-term knee injury.

It is the latest blow in a difficult year, which has also included splitting with coach Dimitri Zavialoff for a second time.

There was a huge positive earlier this month when she beat Ukraine's world number five Elina Svitolina in Montreal, but she then pulled out of her following match against American teenager Coco Gauff.

Konta, who reached the US Open quarter-finals in 2019, returned to action at the Western and Southern Open a fortnight ago, losing to Czech Katerina Muchova in three sets.

Meanwhile, Emma Raducanu's scheduled first-round opponent Jennifer Brady - the 13th seed and Australian Open runner-up - has withdrawn because of a knee injury.

The British teenager will instead play Swiss world number 128 Stefanie Vogele on her overseas Grand Slam debut.

Raducanu, 18, is aiming to back up her Wimbledon exploits - where she reached the last 16 as a wildcard - after coming through qualifying in New York.

After initially being set to play American Brady on Arthur Ashe Stadium, Raducanu now faces Vogele on court 17 at around 19:00 BST on Tuesday.

More to follow.