McLaren Automotive's Driver Development Programme has been suspended for 2020 amid the coronavirus pandemic.
Four new drivers chosen to be part of the scheme at the end of last year were set to race in British GT this season with Tolman Motorsport.
Ginetta GT5 Challenge graduate Katie Milner, former BRDC British Formula 3 racer Harry Hayek, and ADAC GT4 race winners Alain Valente and Michael Benyahia were due to share two McLaren 570S GT4 cars in the series this year.
The manufacturer now intends for all four drivers to instead race in British GT in 2021. McLaren explained the decision has been taken because various elements of the Driver Development Programme - including tailored driver coaching - are not possible at the current time amid social distancing restrictions.
Ian Morgan, director of motorsport for McLaren Customer Racing, said: "This has been a difficult decision and has not been taken lightly, but our ability to facilitate a full Driver Development Programme in 2020 has been limited beyond our control by the ongoing impact of the COVID-19 pandemic.
"We felt our current driver line-up would not receive the full benefit of the programme as it was intended, including the contribution from Tolman Motorsport, which has helped facilitate the smooth running of the programme on track with professionalism and attention to detail.
"We are now focusing on plans for next year and I am pleased to confirm that we will retain the four drivers in the 2020 line-up into 2021."
Tolman is now seeking alternative drivers for the two cars this year, with the British GT season due to begin at the start of August.
Tolman boss Christopher Tolman added: "Clearly this is a disappointing situation, but we fully support this difficult decision; it would not be right to continue in current circumstances and compromise the programme."