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Raikkonen's participation at next weekend's Italian Grand Prix at Monza, the fastest track on the calendar and a home race for Alfa, is also in doubt as the Finn cannot return to the paddock until he receives a negative test.
The 39-year-old Finn's victory for Ferrari in Sunday's US Grand Prix ended a winless run of 113 races dating back to victory with Lotus in Australia in March 2013.
Raikkonen posted a message on Instagram announcing he would be rejoining Sauber on a two-year deal. The Finn first drove for Sauber in 2001.
Raikkonen, the 2007 world champion who is now 41, holds the records for most races entered (327) and started (324) by any driver in the history of the sport and is the oldest on the starting grid.
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