The Enstone-based team had hoped to get the revised E21 ready in time for this weekend's race in Belgium, but it failed to complete all its necessary test proofing beforehand.
Sources have revealed that although the car passed all the mandatory crash tests that are required because of the scale of the revisions, there was an issue with reliability proofing for parts fatigue that meant the team did not wish to risk running it at Spa.
Lotus is confident that the matter will be sorted in the next few days, which means the tweaked car should be ready to race for the first time at Monza.
It is expected that the changes planned for the Italian Grand Prix will be the last major tweaks for this season, as its development focus switches onto 2014.
Lotus owner Gerard Lopez told AUTOSPORT recently that an update programme would remain in place, but it would not be as extensive in the closing stages of the campaign.
"In the second half of the season all you are doing is coming up with new wings, you're not look at changing the wheelbase or things like that - those are things you do in the first 10 races," he said.