BMW Sauber protégé Sebastian Vettel could become a permanent fixture on the Formula One grid as early as next weekend if plans to slot him into the Scuderia Toro Rosso line-up come to fruition.

The early retirement of both Scott Speed and Tonio Liuzzi at the Nurburgring appears to have been the last straw for STR bosses Franz Tost and Gerhard Berger, with some reports suggesting that the former came to blows with Speed after the race. The American then claimed on speedtv.com that the squad were making it clear that neither he or his team-mate were wanted in the line-up.

While it is not expected that both drivers will be replaced before the end of the season, Vettel is being widely tipped to replace Speed before the summer is out, with talks apparently underway to get the German in alongside Liuzzi for next weekend's Hungarian race. Vettel already has plenty of testing experience with BMW Sauber and made his race debut as a stand-in for the injured Robert Kubica at Indianapolis, scoring a point.

Despite rumours that he is being lined up to be a part of its 2008 pairing, BMW is apparently willing to release the German to STR, which is backed by his personal sponsor, Red Bull. Any decision hinges on timing, however, with Berger telling Germany's Auto Motor und Sport that he would be reluctant to run the teenager without any testing. STR could run at Mugello before the Hungaroring round, but a decision would have to be taken immediately for Vettel to benefit from seat time, as there is no testing allowed during the summer break between Hungary and Turkey.

"Vettel is a meaningful alternative for us, but he needs a test before he races," the Austrian veteran confirmed, "It would make no sense to throw him in at the deep end."

Vettel has been mentioned in connection with an STR seat for 2008, when he could team up with Champ Car champion Sebastien Bourdais, but a lot depends on whether BMW Sauber intends to use his talents. Team boss Mario Theissen refuses to be drawn on his line-up for next season, with doubt still surrounding the status of Nick Heidfeld. The German has been enjoying his best season since graduating to F1, but has yet to be offered a new contract. Team-mate Robert Kubica is, like Vettel, a Theissen protégé, and is expected to remain on board for another year.

How joining STR would impact on Vettel's World Series by Renault ambitions remains to be seen, especially as the German currently leads the WSbR standings by 23 points after a strong debut campaign with Carlin Motorsport. There are two scheduled date clashed between F1 and the World Series, meaning that he would have to choose between Monza and Donington Park, and Interlagos and Estoril, before the season is out.

STR has an option on Bourdais that extends only until the end of July, but the Frenchman is expected to be confirmed as part of the team's 2008 line-up, which could effectively spell the end, albeit temporarily, of Liuzzi's F1 career. The Italian had been touted for a switch to Red Bull Racing but, with Mark Webber and David Coulthard already confirmed for next season, the best the Italian could hope for would be a testing berth with a view to resuming his racing role in the future.

Liuzzi was slammed by Berger for joining Speed on the sidelines in the chaotic opening laps at the Nurburgring on Sunday, the Austrian denying claims that the power steering system had failed on the STR02.

"There were extremely difficult conditions at the Nürburgring, and these accidents can happen, but we were once again the only team that lost both cars through accidents - and that is unacceptable," he said, "We checked the systems on Liuzzi's car and all was in order. He just stood full on the gas as he exited the pits and the extra power was too much for the conditions."