The eight-time world champion made his MotoGP debut at the Valencia test in 2012 with the factory Honda team after stepping up from Moto2 as the title winner.
He spent 11 seasons with Honda, winning 59 grands prix and six world titles in seven years between 2013 and 2019.
Since badly breaking his right arm at the Spanish Grand Prix in 2020, Marquez has struggled to recapture that form – first through a lengthy recovery and multiple surgeries, and then due to the Honda's lack of competitiveness.
This reached its nadir in 2023, with Marquez scoring just one grand prix podium in 20 rounds and surpassing his season record for crashes at 29 – five alone coming in a German GP weekend in which his future with Honda became seriously in doubt.
After the Japanese GP, he informed Honda that he would be quitting his contract a year early and subsequently signed with Gresini to race a year-old Ducati for 2024.
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Marquez was granted permission by Honda to ride the Ducati at the post-season test in Valencia on 28 November, despite still being under contract until the end of the year.
On Tuesday morning, he took to the track on a blacked-out 2023-spec Gresini Ducati, with it thought to be the bike Johann Zarco rode this season at Pramac.
Marquez will not speak to the media after the test on Tuesday due to his contractual situation with Honda.
He will leave behind most of his Honda crew, bringing only tyre technician Javi Ortiz to Gresini with him, while his new crew chief will be Frankie Carchedi – who worked with Fabio Di Giannantonio in 2023 and previously with Joan Mir at Suzuki from 2019 to 2022.
Tuesday's Valencia test will also see Luca Marini make his Honda debut as Marquez's replacement, with the Mir taking over the latter's technical crew.
Zarco will make his first Honda appearance since the 2019 Valencia GP with LCR, while Franco Morbidelli swaps the factory Yamaha for the Pramac Ducati.
Alex Rins will ride the Yamaha for the first time, while Pedro Acosta will make his public MotoGP debut with Tech3 GasGas. Di Giannantonio will take to the track with VR46.
