Toro Rosso team principal Franz Tost says there is a four-man shortlist for the second seat in 2015.

Sebastian Vettel's departure from Red Bull and Daniil Kvyat's subsequent promotion has left a seat available alongside 17-year-old Max Verstappen next season. Tost has confirmed that current driver Jean-Eric Vergne - originally set to be dropped next year - is now back in the frame alongside three other Red Bull young drivers.

"The situation is still open," Tost told the official Formula One website. "I think the drivers that are shortlisted for Toro Rosso are: Jean-Eric, Carlos Sainz, Pierre Gasly and Alex Lynn. All four are Red Bull drivers and it will definitely be a Red Bull driver."

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And Tost said he would like to see Vergne retained but admits he doesn't have the final say on who his drivers are.

"I am still convinced that Jean-Eric can do a very good job in Formula One if he gets a competitive car. He has shown this a couple of times and I personally would like to continue with him - but we have to wait to see what Red Bull decides."