News broke on Tuesday morning that Lewis Hamilton will miss the Sakhir Grand Prix after testing positive for COVID-19, leaving a space to fill in the most competitive car on the grid. It's rare that such an opportunity comes up and Mercedes is clearly considering its options after confirming an announcement would be made "in due course".
We take a look at the likely candidates below...
Although Mercedes is in no way obliged to select him, Vandoorne is the team's reserve driver and has attended a number of F1 races this year in case one of the drivers was unable to race. He last raced in Formula One in 2018, scoring 12 points in an uncompetitive season alongside Fernando Alonso at McLaren, before being dropped from the team as it opted for Lando Norris and Carlos Sainz in 2019.
He now races for Mercedes in Formula E, where he won the final race last season and finished second in the drivers' championship. When the news broke on Tuesday he was testing Mercedes' Formula E car in Valencia, but already had a flight booked to join the F1 team in Bahrain ahead of this weekend's race.
His time spent in the Mercedes F1 simulator this year means he would be up to speed with the W11 (at least in a virtual environment) and would have a head start over most drivers when it comes to steering wheel buttons and team procedures.
But the fact he wasn't the automatic replacement when Mercedes announced Hamilton's positive test hints at the team exploring all avenues before committing ...
Although he is a Williams race driver, Russell is managed by Mercedes and remains contracted to the world champions on a long-term deal.
He is already being talked about as a potential replacement for Valtteri Bottas in 2022, so what better chance to put the two drivers head-to-head in a straight fight than now?
The only problem is that Mercedes would have to negotiate Russell out of his Williams contract for at least one race, possibly two. Russell has been Williams' shining light in 2020 and remains the backmarker's best chance of snatching a point before the end of the season.
So a lot will depend on the small print in Russell's contract, or failing that, the financial offer Mercedes is willing to put on the table to secure his services -- not to mention the replacement Williams would need to find.
After his three outings with Racing Point earlier this year, replacing Sergio Perez and Lance Stroll when they had COVID-19, Hulkenberg was dubbed F1's unofficial super-sub.
But the German does not have historic ties to Mercedes in the same way as he does with Racing Point, so he would need to be picked purely on merit and driving skill.
He can make a good argument based on his third-place qualifying result for Racing Point at Silverstone in August and his two points finishes with the team at the 70th Anniversary and Eifel Grands Prix, but Mercedes has already secured both championships so isn't desperate for points.
It would seem strange to pick Hulkenberg when there is at least one driver from Mercedes' own stable ready to go, but 2020 has been full of surprises.
Gutierrez is Mercedes' other official reserve driver alongside Vandoorne, but it became clear earlier this year that his lack of F1 action over the past four years would make him ineligible to renew his superlicence.
He was initially a candidate to be Perez's replacement at Silverstone when his fellow Mexican tested positive for COVID-19, but when Mercedes looked into his eligibility as a reserve it found that he would not qualify for a super licence renewal.
"I think Esteban would have been in a really strong candidate for the seat, but unfortunately he didn't qualify," Mercedes team boss Toto Wolff explained at the time.
"There is a new rule this year that if you haven't raced in a Formula One car in an official event for the last three years or you need to have done a test of at least 300 kilometres."
Gutierrez last race in F1 in 2016 and, regardless of his eligibility, was always going to be a distant second choice behind Vandoorne.