Marco Simoncelli testing WSBK Aprilia.

Mattia Pasini isn't the only 250GP star testing at Mugello this week, with reigning champion Marco Simoncelli also on track - riding Aprilia's RSV4 World Superbike machine.

Simoncelli's presence at the private test has been confirmed by the Mugello Circuit website, although - unlike for Pasini, who is testing the Ducati MotoGP machine - no lap time was given.

Simoncelli's test has fuelled rumours that he will make his WSBK debut at Imola this weekend, riding in place of the injured Shinya Nakano and alongside Max Biaggi.

After crashing at the recent Misano round, the #58 has slipped 40 points behind 250GP title leader Hiroshi Aoyama with four rounds to go.

Simoncelli first rode the V4 four-stroke during a test at Valencia in late 2008 (pictured). The Italian is expected to test the machine at Mugello again today (Wednesday).

Simoncelli rides for the Gilera - which, like Aprilia, is owned by the Piaggio Group - in 250GP, but will switch to Honda for his 2010 MotoGP debut.