Red Bull's plans for the 2019 Formula One season were hampered on Friday as Daniel Ricciardo confirmed a switch to Renault.
Ricciardo's future had long been the source of speculation, but it had appeared as though he would be renewing his Red Bull deal rather than moving on.
The Austrian outfit must now identify a replacement to feature under star youngster Max Verstappen, whose considerable shadow may well have impacted Ricciardo's decision.
Red Bull team principal Christian Horner said in a statement: "We will now continue to evaluate the numerous options available to us before deciding on which driver partners Max Verstappen for the 2019 season."
With rumours of interest in various drivers sure to follow, we have assessed the potential candidates.
Carlos Sainz Jr
With Ricciardo joining Renault, Carlos Sainz Jr - on loan with the French team - will be on the move come the end of the season. Already contracted to Red Bull, he is the obvious option to replace Ricciardo in what would be a straight switch.
Horner and Co. will no doubt have kept a close eye on Sainz this year as speculation surrounding Ricciardo wore on, and he can only have been impressed by the Spaniard's steady displays.
Sainz has completed all but one race, finishing no lower than 12th all season. At 23, he has time on his side, too.
While Sainz is the obvious option, Horner's statement did say that Red Bull would be considering all of their various options. However, even if they were to look elsewhere, Pierre Gasly offers a familiar face.
A star with sister team Toro Rosso, Gasly previously served as Red Bull's test driver.
The Frenchman is just 22 years old but has already been mixing it with the big boys in his first full F1 season, finishing fourth in Bahrain, and Red Bull would have a youthful line-up full of promise with Gasly alongside Verstappen.
A shock move?
An incredible swoop for Lewis Hamilton, Valtteri Bottas or Sebastian Vettel seems highly unlikely, but there are other drivers whose futures are not quite so secure.
Ferrari appear set to make a move for Charles Leclerc, with the suggestion being that Kimi Raikkonen would retire, yet Red Bull must surely consider competing for the Monegasque driver. And if that deal is done, Raikkonen has shown himself capable of still competing in F1 this season. A bid for the Finn would be huge surprise but his presence would give Verstappen a famously laid back mentor.