Nasa says work on the Atlantis space shuttle's problematic fuel sensor system will push back the launch of the Columbus lab to perhaps February.
The European module was supposed to fly to the space station on the orbiter in December before erratic sensors led to the lift-off being scrubbed.
There is now an option for a 24 January launch, but February looks more likely.
The space agency says engineers need more time to fix a suspected faulty electrical connector in the system.
The sensors, which sit at the base of the shuttle's giant external tank, are part of a backup emergency system to cut off the orbiter's three main engines if they run out of hydrogen propellant before the ship reaches orbit.
Running the engines without fuel could trigger a catastrophic explosion.
Recent issues
For more than two years now, these eco-sensors, as they are known, have intermittently given out false readings.
Technicians think they know the source of the problem but admit to being puzzled over why a "design fault" should only recently start to create issues after many years of normal behaviour.
Nasa flight control teams and ground operations teams have been told to be ready for a 24 January launch date. As work progressed on the fuel sensor system, that date would be modified as required, said John Shannon, deputy manager for the space shuttle programme.
"Everything has to go exactly right for us to make the 24th," he warned.
Engineers continue to test modifications to the system connector in a simulator as they make those changes on the Atlantis tank itself. The modifications are expected to be in place by 10 January.
"We're fairly confident that if the problem is where we think it is, that this will solve that," Mr Shannon added.
Busy Europe
Officials stressed 24 January was a "no earlier than" date.
"I think it's much more likely that we'll be going to be ready somewhere in the February 2 to 7 timeframe, given that we don't have any more findings as we go through our testing," said programme manager Wayne Hale.
Columbus is Europe's major contribution to the science endeavours on the International Space Station (ISS).
The 12.8-tonne, $1.3bn euro ($1.8bn; £0.9bn) module will carry out studies that would be impossible in the gravity experienced at the Earth's surface.
The laboratory will be delivered and installed by a joint US-European crew on Atlantis.
February is also the current scheduled launch month for Europe's other major ISS venture - the Automated Transfer Vehicle. The 20-tonne space truck will haul supplies to the orbiting outpost on a regular basis, and will become the station's main re-supply vehicle once the shuttle is retired.
The ATV will also have the task of re-boosting the ISS, which has a tendency to drift back to Earth as it drags through the top of the atmosphere.
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