The Finn will race for the Swiss team in 2019 after ending his second spell with Ferrari this season.
Raikkonen is getting his first experience of Sauber’s current set-up in this week’s Pirelli tyre test in Abu Dhabi.
He is driving Sauber’s C37 on Tuesday and completed a first installation lap as soon as the test started at 9am local time.
Raikkonen, who is not wearing Sauber team gear, has since returned to the track and completed 10 laps by the end of the first hour.
He has an unbranded race suit and a black and a simplified crash helmet design like he used at Lotus in 2012.
The 2007 world champion is not the only driver getting experience of his 2019 team early.
Formula 2 champion George Russell has appeared with Williams for the first time ahead of his graduation with the team next year.
Russell’s F2 rival Lando Norris is at the wheel of the McLaren again.
Pietro Fittipaldi has made his F1 testing debut with Haas. The grandson of two-time world champion Emerson has landed a development role with the American team for 2019.
Also driving in the test on Tuesday are Valtteri Bottas (Mercedes), Sebastian Vettel (Ferrari), Max Verstappen (Red Bull), Sergio Perez (Force India), Nico Hulkenberg (Renault) and Sean Gelael (Toro Rosso).
Other drivers set to appear on Wednesday include Pierre Gasly (Red Bull), Antonio Giovinazzi (Sauber) and Carlos Sainz Jr (McLaren).
New Toro Rosso 2019 recruit Alexander Albon is not scheduled to drive at all.