Fierce rivals of Ferrari great Michael during his golden years at the Italian team, McLaren said on Wednesday they would be able to call on Mick's services as part of a deal with engine provider Mercedes.
The 23-year-old German joined Mercedes as a reserve to seven-times world champion Lewis Hamilton and George Russell after losing his race seat with Ferrari-powered Haas at the end of last season.
"Welcome to the family, Mick," McLaren said on Twitter, pointing out also that new team principal Andrea Stella was previously performance engineer to Michael Schumacher at Ferrari.
McLaren had a reserve-sharing agreement with Renault-owned Alpine last season, when Australian Piastri was Alpine's third driver.
McLaren then won a contract dispute with Alpine for Piastri to race for them this year.
Mercedes and Williams shared Nyck de Vries as reserve last season, with the Dutch driver now due to race with Red Bull-owned AlphaTauri.
McLaren also have 2021 IndyCar champion Alex Palou contracted to a reserve role where the Spaniard's schedules allow. Ten of the 23 scheduled F1 grands prix clash with IndyCar.
