Formula 1 teams are currently forced to issue two free practice outings per season to rookie drivers, as mandated in the sporting regulations.
One-off drivers have been happening in F1 for some time, with several high-profile drivers experiencing a practice outing before making a full-time switch to the sport.
In this list, RacingNews365 looks back at drivers that you may have forgotten about after they took part in a race weekend.
Adderly Fong
At the 2014 Abu Dhabi Grand Prix, Fong was handed a free practice outing with Sauber having tested for the team earlier in the year.
Fong completed 25 laps and ended the session in 19th place, 1.7 seconds down on teammate Esteban Gutierrez.
The Hong Kong-licenced driver teamed up with Lotus for the following year as a development driver, but did not take part in another practice session.
Daniel Juncadella
In the early 2010s, Juncadella had a strong reputation amid a successful junior career which included a title in the inaugural FIA Formula 3 European Championship in 2012.
In 2013 he held a test driver role with Williams before moving to Force India in 2015, and it was with the Silverstone-based team that he received his F1 debut.
At the British, Italian and Brazilian Grands Prix, Juncadella stepped behind the wheel of the VJM07 car.
Juncadella is still active in racing, finishing runner-up in the GTD Pro class in the IMSA Weathertech SportsCar Championship last year.
Raffaele Marciello
Marciello prevailed in the European F3 Championship one year after Juncadella and made the step up with GP2 the following season.
In 2015, the Swiss driver took on a test role at Sauber and received four FP1 outings throughout the campaign.
They came in Malaysia, Spain, Great Britain and the United States.
However in early January 2016, Sauber and Marciello parted ways. The 29-year-old is still active in racing and has secured a Hypercar driver with BMW in the World Endurnace Championship this year.
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Fabio Leimer
Leimer sits as one of the few champions of the GP2/F2 series who did not make a full-time switch to F1.
However, the Swiss driver secured a test and reserve driver position with the now-defunct Manor team in 2015.
Leimer made his one and only FP1 appearance at the 2015 Hungarian Grand Prix - a sad weekend for the sport as it was the first event following the passing of the team's former driver Jules Bianchi.
Alfonso Celis Jr.
Despite having the most FP1 appearance of any driver on this list, Celis Jr.'s F1 participation went largely unnoticed.
The Mexican driver linked up with Force India in 2016 and he was handed six FP1 outings during the campaign.
Celis Jr. was retained for the 2017 campaign and had three more outings that year, including at his home event in Mexico (which unfortunately ended in a crash).
Celis Jr.'s racing career tapered out soon after with two IndyCar outings in 2018 marking the last of his competitive activities.
Naoki Yamamoto
Yamamoto spent his entire racing career in Japan but found great success in his home country.
Having raced in Super Formula and Super GT since 2010 (where he remains to this day), Yamamoto was handed an F1 opportunity in 2019.
With Honda's F1 success growing, Yamamoto got behind the wheel of the Toro Rosso challenger at his home event in Suzuka.
Yamamoto impressed as he clocked in just one-tenth of a second behind teammate Daniil Kvyat.
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