Caterham are closing in on completing their driver line-up for the 2013 Formula One season, but they have also been handed another vacancy to fill.

The Hingham-backed team has already confirmed Charles Pic as one of its two drivers for the new season but is yet to announce its other driver, with the first winter test under a month away.

The battle appears to be between Russian Vitaly Petrov, who drove for Caterham in 2012, and Bruno Senna as he looks for a new team following his release by Williams.

It was Petrov who booked Caterham's recovery to 10th in last season's constructors' championship with his excellent drive in the 2012 Brazilian final�, and with the Russian Grand Prix set to be reintroduced to the F1 calendar in 2013 there are clear plus points.

However, it may be Senna can offer the bigger budget for Caterham to play with in what will be their fourth season on the grid.

Finn Heikki Kovalainen's chances of an extended F1 drive with the Hingham-backed team seem to be shrinking, while Caterham's GP2 racer Giedo van der Garde is also seen as a long shot for the drive.

Force India's second seat alongside Paul di Resta remains the only other drive to be confirmed for the new season.

• Meanwhile, Caterham's sporting director Steve Nielsen has resigned from the team.

Nielsen originally joined at the end of 2011 after a lengthy spell with Renault, and his arrival came with high expectations for what he could bring.

However, it is believed Nielsen will now move to another team after leaving Caterham this month. His replacement at the Hingham-backed outfit is yet to be appointed.