DTM convert Scherer was set to share United’s #22 Oreca with Phil Hanson and Paul di Resta for the eight-hour race after winning on his WEC debut with the team last time out at Spa.
However, on Friday morning it was revealed in a stewards’ bulletin that Scherer had tested positive for COVID-19 twice in a 48-hour period and that the Swiss driver will be replaced for the weekend by Wayne Boyd.
The team itself then made a brief statement saying that Boyd is on standby to take up the vacated seat “pending the results of his COVID-19 test taken this morning”, promising a further update “in due course”.
Boyd, 30, is therefore set to make his WEC debut this weekend after years of racing prototypes for United in the European Le Mans Series, Michelin Le Mans Cup and Asian Le Mans Series.
Since 2019 the Ulsterman has mostly campaigned LMP3 cars, but he did a full season in a United-run LMP2 car in 2018 and more recently raced for the team in the Sebring 12 Hours earlier this year.
This is the second change to the United line-up for the Portimao race, as di Resta deputises for Filipe Albuquerque, who is away on IMSA WeatherTech SportsCar Championship duty at Detroit.
Di Resta was replaced by Scherer in the full-season line-up following Hanson’s promotion from silver to gold status over the winter, but the Scotsman will return to defend his Le Mans 24 Hours win in an extra United entry alongside Alex Lynn and a third to-be-named driver.