Travellers have set up a large encampment on the grounds of Central Ajax FC in Warwick - "putting the future of the club in jeopardy", said the club.
The large group, made up of about 28 families, broke into the ground in Hampton Road on Friday.
As part of the process to have the travellers removed from the site, representatives from the club and Warwickshire Police officers went to the ground on Saturday to inform them they would be evicted from the site in the coming days if they do not leave voluntarily.
The club is now waiting on the police to serve a Section 61 notice on the group before the eviction takes place.
But, in the meantime, the club - which is home to 17 football teams of which most are junior sides - is very concerned about the damage that has been caused to its football pitches.
Travellers last got on to and set up a camp at the site four years ago and since then the club, which is run as a non-profit business, has improved its security and invested £30,000 on drainage works to ensure the quality of its football pitches.
But 4x4 vehicles towing caravans have got onto the wet playing surfaces and caused damage which could be difficult to repair in time for the forthcoming football season at a time when the club is collecting registration fees for its players and preparing for the start of pre-season training at the end of the month.
The club is also used as a base for a BBC production crew from time to time and is set to be used as a venue for children's summer activity camps.
A club spokesman, who wanted to remain anonymous, said: "We are in serious jeopardy of not being able to operate as a football club because of the damage they have caused
"They have undone all the good work we have done over the last four years.
"The police have been very helpful but it is a waiting game now.
"We can't get near the site to see the extent of the damage or if anything has been stolen because we have been physically threatened and abused by the travelers and have been told to stay away until they are gone."
A Warwiskhire Police spokeswoman has said: "This was reported to us at around 5.15pm on Friday evening (July 2).
"We are working with the land owners and notice has now been served."