With the news today that Champ Car champion Sebastian Bourdais will test for Toro Rosso this week, the rumour mill has gone into overdrive, as speculation of the final three remaining seats in Formula One increases. In the FIA entry list released earlier this month, all places were filled, all except one at Spyker and both Toro Rosso seats.

While Toro Rosso chief and co-owner Gerhard Berger has strenuously denied rumours that Red Bull tester Robert Doornbos is in the running for one of the seats, no-one can deny that failing to officially confirm either Speed or Liuzzi for 2007 is bad news for the pair. With Neel Jani unlikely to remain on as Toro Rosso tester, the likely scenario is that the refugee of the team will become tester.

Throw Mika Hakkinen into the mix and the perception changes greatly. McLaren have already confirmed all drivers for 2007 - both race and test - meaning there is no room for the Finn at his former team. But if the double world champion is seriously interested in making a return to the sport, open doors at Spyker and Toro Rosso wouldn't be a surprise, especially considering the vast knowledge and experience he empowers.

A Toro Rosso seat though would be the most logical step for the Finn. With Red Bull Racing launching their first Newey-designed chassis early next year, a designer Mika worked with and for from 1998 to 2001, and considering the close working relationship between RBR and STR, it could be in everyone's interest at Red Bull to support the switch.

For Spyker though, Hakkinen would be a great gift. Since buying MF1 in September, the team has announced high-profile signings, most notably the famed British engineer, Mike Gascoyne. Given his great power at producing fast cars, Spyker may feel that relying on drivers like Albers, Monteiro and Sutil as not great value for money, taking Gascoyne's salary into account, which leads us to Hakkinen - a proven driver, fast and experienced, with the knowhow to improve a car, an area in which the above three are, as yet, unproven.

For Bourdais, the likelihood is that the Frenchman will return to Champ Car next year to fight for a fourth successive title, leaving his dream of a Formula One drive unaccomplished. Toro Rosso however lack any experience, with a combined total of only 40 races in their drivers. Bourdais, although without a Formula One start, has experience in Champ Car, and showed promise by winning F3000 in 2002, and with drivers like Montoya coming straight from America and impressing over here, a switch for Bourdais isn't totally out of the question. The 27-year-old would most certainly have more racing experience than Speed, who has been targeted as the weaker of the two drivers, by none other than his Team Principal, Gerhard Berger.

But it could just as easily happen that Hakkinen returns to DTM and Bourdais returns to America as planned, and Liuzzi, Speed and Monteiro are signed up at their respective teams, especially considering the former has stated for months that only small contractual issues have prevented an official announcement on his signing.

For now though, watch this space...