While Carlos Sainz and Lando Norris will share testing duties, the Spaniard driving the MCL34 on Tuesday morning and the Briton that afternoon and all day Wednesday, Fernando Alonso will also be at the wheel of a 2019 car, albeit on tyre testing duty for Pirelli.
The Spaniard will drive the car all day on Tuesday and Wednesday afternoon, with countryman Sainz driving the car on Wednesday morning.
When Alonso walked away from F1 at the end of last season, the door to a return was conveniently left ajar, neither McLaren or Alonso fully committing to a clear answer on whether such a return was possible.
The test will not only allow Alonso to try the 2019 chassis with the new aero regulations, but also sample prototype 2020 tyres ahead of a possible return next season.
For McLaren, Alonso's time in the car will allow the Woking outfit to learn from the two-time world champion's vast experience as he compares the MCL34 to its predecessor.
While the move means that McLaren will have to run a young driver at the subsequent test in Barcelona, albeit for just half a day as Norris will not have contested more than two Grands Prix ahead of the Bahrain test, there is every possibility that Alonso will participate in the post-Abu Dhabi tyre test.
Check out our Thursday gallery from Sakhir, here.