Mercedes suffered the first power unit-related issue just after two and a half hours of testing during the first day of pre-season tests in Bahrain.
The morning session of the pre-season testing kicked off at 7:00 GMT. Mercedes was the first car on track, as the German team couldn't wait to get on with their testing procedures.
There are three days of testing in total, which have to be split equally between Gerger Russell and Lewis Hamilton, and Mercedes decided to dedicate the whole first day to the younger of the pairing.
The 25-year-old surely also couldn't wait to put in as many laps as possible ahead of the season's first race, which takes place at the same track - Bahrain International Circuit next week.
All drivers effectively have only one and a half days' worth of preparation before the first Grand Prix weekend, so every single lap counts for getting more familiar and confident inside their 2024 challengers.
However, Russell's and Mercedes's progress was hindered around midway through the session as he encountered problems with the hybrid system and had to come into the pits to get his W15 fixed.
It was first expected to take around 90 minutes to fix the issue, but in the end, it took a little over one hour before the Briton got to sit back in his car.
As a result, George Russell was the second driver with the least laps, right after Alex Albon, who retired from the session due to unknown reliability issues.
Russell completed only 47 laps, which is 30 less compared to Fernando Alonso, who made the most of the morning session out of all the drivers on the grid.
The 25-year-old will, fortunately, get more time during the evening session, which begins at 12:00 GMT, as he is one of only two drivers on the grid, including Max Verstappen, who get to drive throughout both morning and evening sessions today.