Boeing is warning that deliveries of its 787 Dreamliner may be delayed after a series of battery mishaps grounded its fleet in January.

The company told two European airlines on Friday that deliveries may be reschedule as it re-tests the troubled aircraft and awaits approval from the Federal Aviation Administration. The FAA suggested Thursday the design or manufacture of the Dreamliner’s lithium ion battery may be at fault for its problems.

Norwegian Air said Boeing has alerted the company to a possible delay of its first 787, which was due in April 2013, and may also push back its June delivery.

“We deeply regret the impact the recent events have had on the schedule of Norwegian and their customers,” Boeing said in a statement. “We are staying in close communication with the airline as we work towards an approved means of compliance with the FAA Airworthiness Directive and develop a plan for resumption of 787 deliveries.”

Thompson Airways, owned by Britain’s TUI Travel, has also been told not to expect its Dreamliners on time. The company told Reuters a delivery scheduled for the end of February had been “moved out of the month.”

Boeing has not given a revised timeline to either airline, but said it is working to get its fleet operational as soon as possible.

“The company has an extensive team of hundreds of experts working around the clock, focused on resolving the 787 battery issue and returning the 787 fleet to full flight status,” the company said in a statement. “We are working this issue tirelessly in cooperation with our customers and the appropriate regulatory and investigative authorities. At the same time, a dedicated team of professionals is continuing to produce 787s and prepare them for delivery.”