Businesses estimate the ongoing closure of the A591 between Grasmere and Keswick will cost the local economy £100million.
Earlier this month, the Transport Secretary Patrick McGloughlin revealed it won't reopen until the end of May.
South Lakes MP Tim Farron says that'll have a "crippling impact" and has called on the government to fund a temporary solution.
Cumbria County Council is building a temporary road to bypass the collapsed section - but that will only be open to a shuttle bus service.
The A591 has been shut at Dunmail Raise since the damage was caused by Storm Desmond in early December.
Mr. Farron said: “The A591 is absolutely critical for local businesses, connecting the north and south of the Lake District. Without a flow of visitors to the Lake District, local businesses will be driven under. If the road remains closed during April and May, it will cost the local economy almost a million pounds per day.
“A temporary solution to the closure of this road to allow meaningful reinstatement of vehicular access would be a lifeline for local businesses.
“I am calling on the government to provide the funding needed to allow this to happen. The viability of a huge number of local jobs depends on this. Local businesses have already been badly hit by the flooding, and the government should invest the funds needed for this temporary solution to support the local economy.”