SpaceX's new, powerful rocket, the Falcon Heavy, was at its launch pad at NASA's Kennedy Space Center on Tuesday, awaiting an engine test-firing sometime this week.
SpaceX typically supplies such an adapter but reportedly did not for this mission.
A secret spacecraft launched by a SpaceX rocket on Sunday failed to enter a stable orbit and was lost.
SpaceX competes for military launches with United Launch Alliance, a joint venture of Boeing and Lockheed Martin Corp., which was the sole provider for the Pentagon until Musk launched a campaign in Congress and the courts challenging what he called an unfair monopoly.
According to a source, the satellite did not reach the designated altitude and instead, fell back down, along with the expended second stage of the SpaceX rocket.
However, SpaceX seems to be distancing itself from the alleged failure.
"After review of all data to date, Falcon 9 did everything correctly Sunday night".
"We do not comment on missions of this nature; but as of right now reviews of the data indicate Falcon 9 performed nominally", said SpaceX spokesman James Gleeson in an e-mail.
The mission most likely cost billions of dollars, and congressional lawmakers have been briefed on the developments, The Journal reported.
Whether the Falcon 9 Zuma mission failed or not, SpaceX is now setting its sights on the Falcon Heavy debut launch.
The secretive nature of the Zuma payload makes reliable details about the mission hard to come by or verify.
But the spacecraft apparently did not separate as it was supposed to from the upper stage of the rocket and did not reach a stable orbit, according to a US administration official and two sources who were briefed on the matter. The Falcon Heavy is perhaps the most important rocket ever created by SpaceX, as it is the one planned to be used for missions to the moon and Mars.
"It matters for future SpaceX customers who would want to know if SpaceX's payload adapters were unreliable", he replied in a follow-up tweet.
Neither industry nor government officials would comment on the goal of Zuma.
This was just SpaceX's third national security mission and was seen as critically important in winning further lucrative business from the US Department of Defense.
Tim Paynter, a spokesman for Northrop Corp., which was commissioned by the Defense Department to choose the launch contractor, said "we can not comment on classified missions", and army lieutenant colonel Jamie Davis, the Pentagon's spokesman for space policy, referred questions to SpaceX. If we or others find otherwise based on further review, we will report it immediately.