Schumacher took the wheel of McLaren's 2021 MCL35M car on Wednesday as part of F1's so-called TPC rules, which allow tests with two-year-old machinery.
The test is part of Mercedes' arrangement of sharing its test and reserve drivers with McLaren, which takes customer engines from the German manufacturer.
In previous years it had agreed a deal with Mercedes to call upon Stoffel Vandoorne and Nyck de Vries in case it needed to replace one of its race drivers.
For the 2023 season that deal was extended, with incoming reserve driver Schumacher being made available if either Lando Norris or rookie Oscar Piastri is unable to race.
By completing the Portimao test Schumacher was able to get up to speed with how McLaren works, having not operated with the Woking team before.
With McLaren's race team in the middle of a double-header of the Austrian and British grands prix, the team sent out a test team which included some of its young engineering talents.
"Joining Mick are some of our mechanic and engineering apprentices and interns, gaining valuable experience working in a trackside environment," the team explained on Twitter.
It is the 24-year-old German's second F1 test of the year after taking on a day of Pirelli tyre testing in Barcelona for Mercedes, where teams were trialling blanket-less prototype tyres for the Italian supplier.
Talking about the Barcelona test, Schumacher said: "This experience will definitely benefit me in my role.
“I have a better understanding of what to look out for and what to work on. I also have a better understanding of all the procedures and how the team works trackside. That would be a key factor in case I ever have to jump in and race.”
Schumacher moved to a test and reserve driver role after not being retained by Haas, which gave the son of seven-time world champion Michael Schumacher his F1 debut in 2021.
Following two tough seasons with the struggling outfit, Schumacher was replaced by his more experienced fellow countryman Nico Hulkenberg for 2023.
Schumacher will make another F1 cameo later this month when he'll drive his father's 2011 Mercedes W02 car at the Goodwood Festival of Speed.
