Toto Wolff has confirmed that the second seat at the champions will either see Bottas continue for a fourth season, or see Esteban Ocon ascend from his reserve role.
The driver market crashed into action this week with Red Bull promoting Alexander Albon to replace Pierre Gasly for the remainder of the season and the next major decision is Wolff's to make.
Bottas won two of the first four races of the season, putting a winless 2018 to rest, but he has since fallen badly off the pace of Hamilton and sits 62 points adrift of his team-mate over the summer break.
Top seats in F1 are difficult to come by. Ferrari's line-up seems set for 2020, Red Bull remain determined to promote from within and the resurgent McLaren have confirmed Carlos Sainz and Lando Norris will remain, leaving Bottas short of top-level options if Mercedes opt for Ocon.
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