Until 2012, Scotland had two Emergency Towing vessels (ETVs) available to help ships in trouble off the north and west coasts.
One ship continues to operate out of the Northern Isles.
UK transport minister John Hayes said he did not believe a second tug could have prevented the oil rig's grounding.
Transocean Winner ran aground at Dalmore on the Isle of Lewis after breaking free from its towline during stormy weather on 8 August.
Scottish transport minister Humza Yousaf called for a new risk assessment following the incident with a view to re-instating a second ETV.
But in his reply, John Hayes, minister of state at the UK Department of Transport, said it was doubtful whether a second ETV would have made any difference.
He said: "It would have been extremely difficult, even if there had been an ETV in the area, to secure another tow onto the unamnned rig when contending with 40-45 knots of wind in 10 metre seas.
"Attempting to do so, whether by helicopter or boat, would have exposed all those involved to significant and unacceptable danger."
Mr Yousaf said the UK government's response was "disappointing and frustrating".
He added: ""West coast communities have long argued for the return of a dedicated Emergency Towing Vessel to their waters.
"The Transocean Winner incident has served as a powerful reminder that we must plan for the unexpected.
"Scotland's internationally important marine habitats deserve the best possible protection and the thousands who rely on our seas for their livelihoods will understandably feel short-changed by Whitehall."
The next five-year contract to operate the ETV service, which has recently gone out to tender, stipulates that the tug would be required to patrol the whole ETV area, taking account of weather forecasts which might increase the risk of incidents occurring.
Calls for a review of emergency tugboat provision in the wake of the Transocean Winner grounding have been rejected by UK ministers.