RWE, the second largest utility company in Germany and a Nabucco pipeline consortium member, said it was reviewing its finances when considering the $10.4 billion project.
"In the changed circumstances with new gas pipeline projects in view, we are revising whether Nabucco will take our proposals into consideration," Russia's state-run news agency RIA Novosti quoted RWE as saying.
Nabucco is seen as a counterpart to Russia's South Stream project. Both would move natural gas through southern Europe in an effort to avoid politically sensitive territory in Ukraine.
Nabucco is plagued by financial doubt, though it's the most ambitious of the projects included in the so-called Southern Corridor of gas transit networks aimed at reducing European dependence on Russian gas.
Nabucco would get the bulk of its natural gas initially from the Shah Deniz field in Azeri waters of the Caspian Sea.
The BP-led consortium managing the natural gas field is expected to make decisions on transit networks this week. Nabucco West, a scaled down version of the larger project, is up against the South East Europe Pipeline, a project backed by BP in September.