Campaigners say they will appeal a judge's decision to refuse permission for a judicial review of Oxford United's new 16,000-seater stadium planning approval.
The club's plans to build on land known as the Triangle, near Kidlington, were first approved by Cherwell District Council and then by the government last year.
Friends of Stratfield Brake (FoSB) first lodged their legal complaint citing potential impact on local wildlife, as well as aspects of the planned road closures, in April after launching a fundraiser to cover the legal costs.
Oxford United previously suggested its future could be in jeopardy if the new ground was not built.
FoSB's request for a judicial review was denied for a second time in September.
The group said in a post they would be lodging an appeal with the Court of Appeal on Thursday.
"Our lawyers have advised that we have grounds to appeal the judge's decision...," the post reads.
It adds they remained "mindful" that any legal challenge was "an uphill battle".
"However, we believe the likely impact of the proposal on the local community, and the potential for damage to the Stratfield Brake woodland, which Natural England's woodland specialists have agreed is probably ancient woodland, make this a battle worth continuing," the post added.
The first appeal failed and the group instead turned to a permission hearing, which took place at the Royal Courts of Justice in September.
The initial decision by Cherwell District Council to grant the stadium planning permission had been delayed after nearby woodland was declared as ancient.
Natural England later reversed this view, saying the trees in question were not found on Oxfordshire maps it had studied from the 18th and 19th centuries.
Oxford United previously said the stadium provided a "once-in-a-generation opportunity".
The Kassam Stadium, the club's home since 2001 which does not have a stand on each side, has a lease that is due to expire in 2028.
Plans for the new stadium, to the north of Oxford and beside the A34, include a 180-bed hotel, restaurant, conference centre and community plaza.
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