The German Aerospace Center (DLR) said on Friday it suspects Philae is now covered in dust and too cold to operate.
"Unfortunately, the probability of Philae re-establishing contact with our team at the DLR Lander Control Center is almost zero, and we will no longer be sending any commands," Stephan Ulamec, Philae Project Manager of the DLR, said in a statement.
Philae came to rest on a comet in November 2014 in what was considered a remarkable feat of precision space travel. But it closed down soon after because it was in the shade and could not be recharged.
The probe woke up in June as the comet approached the sun, giving scientists hope that the lander could complete some experiments that it had not done before its solar-powered batteries ran out.
But the lander has not made contact with its Rosetta orbiter since July 9, and a last-ditch attempt to re-establish contact with the robotic lab has failed.
"It would be very surprising if we received a signal now," Ulamec said.
While the project team believes that Philae is likely ice-free, the solar panels that recharge its batteries are probably covered with dust.
In addition, night-time temperatures can now fall below 180 degrees Celsius below zero (-292 degree F) as comet 67P/ Churyumov-Gerasimenko moves away from the sun, which is much colder than Philae was designed to withstand.
While Philae did not have as much time as initially hoped after landing for experiments, information it has collected is reshaping thinking about comets, and it has been a useful lesson for designing future missions.
Scientists expect to get a final glimpse of the lander in the European summer, when the Rosetta spacecraft snaps some pictures during close fly-bys, before landing on the comet itself when its mission ends in September.
And in around six years, Philae and Rosetta will near the Earth again when the comet returns to circle the sun again.
Rosetta is a mission of the European Space Agency, with contributions from its member states and US space agency Nasa. The Philae lander was provided by a consortium headed by the DLR.
© Thomson Reuters 2016