Industry experts have suggested that a United-Continental combination makes more sense in part because of the two carriers already cooperate with each other.
If United and Continental were to complete a deal, it would create the world's largest carrier, leapfrogging over Delta Air Lines.
In a memo to employees, US Airways CEO Doug Parker said that the carrier continues to believe in the merits of consolidation, but for the foreseeable future it intends to remain a standalone carrier.
"As I have said many times, it is not necessary for us to be direct participants in a merger because the entire industry benefits when consolidation occurs," Parker said.
US Airways shares fell 27 cents, or 4 percent, to $6.49 in morning trading. Shares of UAL, United's parent, rose 23 cents to $21.66