Test driver Rodolfo Gonzalez was always scheduled to replace Bianchi for practice one, but the Frenchman only managed a handful of laps in the second session.
"He just had a stomach bug overnight," team boss John Booth told AUTOSPORT.
"He is feeling very weak and hasn't eaten anything today so we have gave him two short runs just to get him ready for tomorrow. We did three laps on primes and three laps on options."
Asked if he was worried Bianchi might be ruled out for the weekend, Booth replied: "No. The doctor has been down and he has got no infection."
Booth said Bianchi "would have struggled to drive" in the morning given his condition, so Gonzalez's pre-arranged presence was a relief.
"It was a fortuitous coincidence," he said.
- Rodolfo Gonzalez