Sebastien Loeb will test Citroen's 2017 World Rally Car on gravel for the first time on Wednesday.
The nine-time WRC champion returned to Citroen last month try its C3 WRC on asphalt, and will spend a day on gravel close to Barcelona as part of the team's pre-Rally of Spain testing.
Citroen team principal Yves Matton said he was looking forward to Loeb's feedback, saying: "It was useful to take his feelings from the test on tarmac and it will be the same when he drives on the gravel."
Motorsport.com understands the potential for Loeb to return to Citroen for a limited programme of WRC rounds next season depends largely on the result of the Spanish test.
Loeb won all nine of his WRC titles with Citroen from 2004-12 before branching out into circuit racing in 2013.
He joined the French marque's WTCC programme in 2014, but was dropped at the end of 2015 before moving across to sister brand Peugeot to focus on World Rallycross and rally-raid programmes.