Veteran Formula One team chief Peter Sauber said on Saturday that he did not believe Renault's newly-promoted Brazilian 'pay driver' Bruno Senna could match dumped German Nick Heidfeld for driving skills.
In an interview with Blick newspaper, he said he thought the decision to change drivers midway through the season was "only about economic problems."
Sauber's Swiss team are in a close fight with Renault in the 2011 constructors' world championship.
Sauber said: "I do not expect that Senna can offer the team (Renault) the same driving skills as Heidfeld."
Germany's Speed Week reported that Heidfeld, 34, a veteran of 183 Grands Prix and two long spells with the Sauber team, is seeking full payment of his fees - 260,000 euros per race - for the remainder of the calendar.
Heidfeld claims breach of contract. With eight races remaining, that adds up to more than two million euros.
The case is due to be heard in the High Court in London on September 19.
"This position (the appointment of Senna) is disputed by the team for apparently purely financial reasons," Heidfeld's lawyer Stefan Seitz said.
Heidfeld said: "I still have a clear contract and I want to drive. A racing driver always wants to race and that's why I'm not at all upset at Bruno. He obviously wants to race as well."
Senna, the nephew of the legendary late Ayrton Senna, has struggled in poor weather conditions in Belgium this weekend. He has one season of experience in Formula One with the Hispania team and has yet to score a point, but has a substantial portfolio of personal sponsors.
Heidfeld, a contracted driver, has scored 259 points, but has never won despite finishing second a record eight times.