McLaren boss Eric Boullier has confirmed that the team were forced to delay the planned upgrade in Australia because of their reliability woes in winter testing.
The Woking team endured another torrid pre-season as McLaren admitted they pushed the limits too far on the new MCL33 in Barcelona.
And that meant McLaren were unable to arrive to the season opener in Australia with a full implementation of their projected upgrade.
"We were obviously not prepared for Barcelona and I'm glad we fixed the reliability issues for the weekend," McLaren racing director Boullier told Motorsport.com.
"But during the last few weeks [before the race] we spent our energy fixing the reliability issues and not bringing the upgrade faster to the track.
"So we are going to have another batch coming in Bahrain, which should have been in Australia."
That new batch is set to include a new bargeboard update which is believed to be worth a few tenths.
Boullier also suggested that it might take up to as many as five races for McLaren to catch up.
"I don't know but I would say the usual answer which is first European race," he added.
"It's the catch up point where you get back to where you should have been."