Mercedes DTM boss Norbert Haug wants to wait for Ralf Schumacher to decide whether he wants to race in the DTM this year before finalising the team's driver line-up.
After the former Grand Prix driver sampled a 2006-spec C Class at Estoril this week, Haug said: "I don't want to raise high hopes. He is testing and to date nothing else has been discussed.
"Should he be inspired by the tests and the same can be said about us, then it's time to continue the discussions."
But Haug denied that Mercedes is looking for an ex-Formula One driver to replace Mika Hakkinen, who retired at the end of last season: "The series is strong enough, we don't need to hire people just for their names," he said.
"I've known Ralf since he was in F3, and for many years he said he'd like to try the DTM. I said he should wait until his current contract situation allowed it and this is the first opportunity."
Mercedes also tested fellow F1 refugee Christian Klien and F3 graduate Maro Engel alongside regular drivers Bernd Schneider and Bruno Spengler at Estoril.