KTM had planned to run three bikes at its home race but with test rider Mika Kallio also out of action after a nasty crash in Germany in July which required surgery, only Bradley Smith rode an RC16 at the Red Bull Ring.
Despite signing Randy de Puniet to fill Kallio's testing duties for the rest of the year, the Frenchman effectively ruled himself out of a race start due to his unwillingness to do so without testing prior to arriving at Silverstone.
KTM has instead opted for his countryman Baz, who is currently riding for Althea BMW Racing Team in the Superbike World Championship.
“Pol was hoping to ride but his recovery still needs a bit of time,” explained Baz.
“I would therefore like to wish him a speedy recovery.
“My manager informed me about this opportunity on Monday afternoon and the agreement was reached very quickly.
“I would like to thank Genesio Bevilacqua (team principal) from team Althea BMW Racing for allowing me to race at Silverstone.
“I am pleased that KTM thought about me, because it is a big team. I will make the most of it, enjoy it and try to have a good weekend. I am not setting myself any objectives.”
Baz is currently 12th in WorldSBK.
The 25-year-old spent the previous three years in MotoGP, with best finishes of fourth in each of the 2015 San Marino race and 2016 Brno race.
Practice at Silverstone starts on Friday evening before qualifying from 2310 AEST on Saturday night.