Apr.3 (GMM) Ralf Schumacher has refused to rule out returning to formula one.

The winner of six grands prix left the series at the end of last year following three consecutive disappointing championship campaigns with Toyota.

But unlike his brother Michael, who voluntarily retired as a seven time world champion in 2006, 32-year-old Schumacher does not consider his professional motor racing career to be over.

Ralf has signed up for the competitive German touring car series DTM with Mercedes-Benz for 2008, and he intends to try to capture the attention of his former F1 contemporaries.

"I am totally concentrated on the DTM," he said in an interview with the news agency SID.

"Of course, I would have been happy to continue in formula one with a competitive car, but now a new challenge begins for me," Ralf, who tested unsuccessfully with the Force India team in the 2008 pre-season period, added.

Now part of the Mercedes family, Schumacher admits to some feelings of envy when he watched Lewis Hamilton and Heikki Kovalainen debut the competitive McLaren MP4-23 last month.

"It would really excite me to race that car. Should I ever get the chance to get back into formula one competitively, Mercedes would certainly not stand in my way," he said.

He confirmed that he is only committed contractually to the DTM series for 2008.

"What comes afterwards, I will decide with Norbert Haug at a later date," Ralf Schumacher said.