Ryan Briscoe is the lead candidate to replace Sam Hornish Jr in the IndyCar Series if the American switches to NASCAR, this week's Autosport reports.
Three-time IRL champion Hornish has been tipped to move to NASCAR next season after making a handful of Busch Series starts this year with Penske, while Briscoe currently races for the squad in the American Le Mans Series.
Briscoe made a one-off open-wheel appearance at the Indianapolis 500 in May, where he finished fifth with Penske equipment, driving for a team run by Roger Penske's son Jay.
Penske Racing president Tim Cindric said: "At the point where we make that decision if that seat is open, Ryan is certainly the lead candidate to do that."
Hornish will make his Nextel Cup debut at New Hampshire on September 16, but a permanent switch to the series has not yet been confirmed.
Briscoe said: "I'm waiting to see how things evolve from now and I really have no idea. They would be big shoes to fill."