Briton Horner, boss of McLaren's arch-rival, blamed the Woking based team for Mark Webber's Melbourne woes.
Australian Webber had a terrible start and then a KERS issue in his home race, and Horner said afterwards: "You need to ask McLaren why the ECU didn't work because he was blind and had no telemetry.
"It is something they need to get on top of because it caused a lot of issues during testing," he added.
Horner is referring to the standard electronic control unit mandatorily supplied by McLaren subsidiary MES to every team in F1.
As for McLaren's disastrous new 2013 car, there is talk of reverting to last year's winning machine, but it is believed that the British team is more likely to try to improve the MP4-28.
Triple world champion and Mercedes team figure Niki Lauda tipped McLaren to bounce back.
"McLaren is famous for responding quickly to problems. It is impossible to write them off," he said on German television RTL.