Amos, 22, was expected to return in February after injuring a shoulder in the 32-8 loss to Australia in November.
But the Dragons say he is unlikely to be back until at least April.
"We're optimistic we will see him before the end of the season but it's unlikely for March," said elite performance manager Huw Bevan.
It is a blow for the 11-times capped Amos, but Bevan aimed to put a positive spin on his return.
"Hallam is making good progress and we will decide in conjunction with the Welsh Rugby Union when he will return to play," added Bevan.
Another Dragons wing sidelined is Ashton Hewitt, who has yet to recover from the concussion he suffered on New Year's Day against the Cardiff Blues.
Hewitt is still undergoing return to play protocols and has been ruled out of Saturday's Pro12 trip to Glasgow.
The region hope he will be fit to face Ulster on 24 March.
The uncapped 22-year-old was named in the Wales Six Nations squad, but is now back in the care of the Dragons.
"With a head injury you have to be careful and there are protocols that you have to follow," said Bevan.
"He is improving but hasn't quite managed to complete the full return to play protocol.
"It's just going to be a matter of time and because he is making progress everybody is optimistic and positive that he will return shortly."
Scrum-half Tavis Knoyle misses the Glasgow trip with a wrist injury, while full-back Carl Meyer will also be absent after failing to pass return to play protocols following a blow to the head in the heavy home defeat against Leinster last Friday.
The Dragons are also without Wales lock Cory Hill who has not been released from the Six Nations squad.
Wales wing Hallam Amos' return to action has been delayed after the Newport Gwent Dragons admitted he is unlikely to play this month.