A dual carriageway at the Brighton and Hove Albion's proposed new stadium would turn a country road into an urban highway, a public inquiry heard.
Hillary Leigh, representing the Society of Sussex Downsmen, said Village Way acted as a "valuable punctuation mark" between Brighton and Hove and the South Downs.
She said widening the road would eliminate the green gap which protects Falmer village.
The inquiry is sitting for an extra two weeks to consider highway improvements needed to secure the University of Brighton's support for the 22,000-seat stadium at Village Way North, Falmer.
Mrs Leigh said: "The society considers that these road proposals would add to the impact of the stadium on the Downs."
She said the Countryside Agency wanted greater weight attached to the value of the South Downs around the proposed stadium.
She said: "The agency's view, with which I wholly agree, is this area forms part of a continuous sweep of open downland."
As well as widening Village Way, the club proposes a roundabout with the junction of the B2123.
Jonathan Clay, representing the club, said the roadworks would not have a significant impact, and Village Way was a modern road and lacked rural character.
He said: "It is not a historic road that has followed contours and ancient trackways."
The inquiry is due to end tomorrow. The planning inspector expects to send his report to Deputy Prime Minister John Prescott before the end of the year.
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