Cristiano da Matta has been dropped by Toyota for the rest of the Formula One season, with test driver Ricardo Zonta called up as his replacement, while Williams have announced the return of Ralf Schumacher will be delayed by at least two weeks.
Da Matta has endured a difficult term and will leave Toyota at the end of the season when Ralf Schumacher and, almost certainly, Jarno Trulli are drafted in.
But Toyota have today ended the Brazilian's season early by dropping him from their race driver line-up in favour of countryman Zonta, the team's third driver this year.
Schumacher has been out of action since cracking vertebrae in his back at Indianapolis in June but hoped to return next weekend in Hungary.
"Ralf's bone thickness was measured and it was established that the two broken vertebrae were not yet as hardened as is normally the case," his manager Willi Weber told German newspaper Bild. "Another accident like the one in Indianapolis and Ralf could be made a paraplegic. Nobody could accept that."
Schumacher 's replacement for the Hungarian Grand Prix will be announced later today with Antonio Pizzonia expected to continue as stand-in.
Toyota team boss Tsutomu Tomita revealed that disappointing form was the motivation behind da Matta's demotion, with the former Champ Car title winner having scored three points this year to team-mate Olivier Panis's five.
"We revised our original plans after we reviewed the results of the last three grands prix," said Tomita.
"Ricardo Zonta consistently performed very well, as indeed he also did in the first half of the 2004 season.
"We believe it is fair to offer Ricardo the chance to show his potential in full race conditions, before we enter into the final step of our driver evaluation for the 2005 season.
"We decided to retain Olivier Panis as a race driver for the rest of this season, based on the fact that he is the driver who has secured the team's best race result of the year so far and has collected the higher number of championship points.
"Cristiano da Matta will remain a Toyota driver until the end of 2004 and could still be called upon to undertake activities accordingly."
Zonta has experience of racing in Formula One having spent two seasons with BAR as well as two races in a Jordan in 2001, his last grand prix outings.
His first chance to show he is ready for a racing return comes next weekend in the Hungarian Grand Prix.
Today's news seemingly closes the door on da Matta's Formula One career, with the Brazilian now expected to return to the United States, where he forged his reputation in Champ Cars.