The first-round match involving Australian Ajla Tomljanovic at the Birmingham Classic has been removed from the schedule because of coronavirus concerns.
The clash due on Monday between world No.72 Tomljanovic and tournament top seed Elise Mertens was replaced by one pitting Harriet Dart against Caroline Garcia.
"A player and coach were identified as a potential close contact on an arriving flight as part of UK's NHS Track and Trace service," the organisers said in a statement.
"While that case is being fully examined, the decision was taken to defer the first-round match between Elise Mertens and Ajla Tomljanovic from Monday's order of play ... ensuring all policies and procedures are appropriately followed."
In her first match in tour since February, veteran Australian Samantha Stosur suffered a 6-3 6-4 defeat to Tereza Martincova.
The 145th-ranked Stosur, who spent 2020 at home through the COVID-19 pandemic, is returning to action from an extended break due to a heel injury that prevented her appearing at the French Open.
Meanwhile, British No.3 Dart suffered a 7-5 4-6 6-4 defeat to France's Garcia in the opening round.
Dart fought back from 5-1 down in the decider with three games in a row but then had her serve broken again as Garcia triumphed.
Former top-10 player CoCo Vandeweghe earned her first tour-level main-draw victory in nearly two years by beating Kristyna Pliskova 6-4 7-6 (7-1) with the help of 13 aces.
Vandeweghe reached two grand slam semi-finals in 2017, at the Australian Open and US Open, and has twice been a quarter-finalist at Wimbledon.
But injuries have hampered the 29-year-old American, forcing her off the tour for extended periods and she now is ranked 203rd
Britain's Heather Watson battled past Viktorija Golubic 3-6 6-2 6-2 for just her fourth tour victory in 2021.
There are tight protocols around all the grass-court events happening in the UK, with players required to stay in designated hotels and only allowed to leave to travel to tournament sites.
Australian Associated Press