Akiyoshi stands in for Aoyama

Aoyama has been diagnosed with a fracture to his T12 vertebrae following his violent crash in the warm-up at Silverstone last weekend.

Team boss Daniel Epp said it would be some time before the 250cc champion was fit to return.

"It really is a pity that Hiro had this nasty crash in Silverstone and that he injured himself so badly, so he will be out for the next couple of months - especially now his learning process was really good and he was consistently getting better," Epp said.

"We hope he will have a quick recovery and that he will be back with us as strong as he was before as soon as possible."

Akiyoshi made four MotoGP starts as a wildcard rider with Suzuki when he was part of its test line-up before switching to Honda last season. He is confirmed at Interwetten for Assen and Catalunya, but Epp said the team had yet to choose a long-term substitute.

"For the meantime we are looking for a stable replacement," he said. "At the moment we don't have a rider apart from Assen and Barcelona and we are looking for a suitable solution."