Shares of the Chicago-based food-delivery company were off slightly to $69.31 in premarket trading.
The companies said the acquisition is proceeding as expected and they have obtained all regulatory approvals required for the completion of the acquisition.
The amendment extending the end date is intended to provide both parties additional certainty regarding the timing of necessary steps to completion, including the registration of Just Eat Takeaway.com ordinary and American depositary shares in the U.S.
The two companies announced the $7.3 billion acquisition in June where Just Eat agreed to pay $75.15 a share for Grubhub in an all-stock transaction.
Last month, Just Eat Takeaway.com reported higher revenue and underlying profit for the first half of 2020, as the coronavirus lockdown sparked a rise online orders and restaurants flocking to its services.
Adults 65 and older increased their digital food ordering by a 428% in June, while online ordering among adults 55 and older jumped by 200%, according to the market research firm NPD Group.
However, several Democratic senators expressed concern about the combination, which would put rival DoorDash at a disadvantage.
Sens. Amy Klobuchar of Minnesota, Richard Blumenthal of Connecticut, Patrick Leahy of Vermont and Cory Booker of New Jersey had urged antitrust regulators to investigate the Grubhub-Uber transaction if it occurred.