Nicky Hayden has revealed that sensor and clutch problems contributed towards a disappointing grand prix debut as a Ducati Marlboro rider in Friday's free practice session at Qatar.

The 2006 world champion, who has moved to Ducati after six years at Repsol Honda, finished the 45-minute session in 13th position, over two seconds behind pace setting team-mate Casey Stoner.

"Today wasn't a great day. To start with I had a problem with a sensor on my first bike and I had to come back after just three laps of my first run and change to my second bike," explained the American. "The set-up wasn't the same and the clutch wasn't quite right. The 45 minutes flew by and we weren't able to get back on the pace we set here in the test.

"Obviously I'm going to need both sessions tomorrow to work something out and get on the pace," he admitted. "Casey and Valentino are already looking really quick but we're not too far off the group behind them. Hopefully with the right changes to the bike tomorrow we can get amongst them."

Hayden, fifth fastest at last month's Qatar test, is presently one second away from fourth placed Jorge Lorenzo.