Southampton City Council said “a direction to leave” had been served to the travellers who pitched up on a cricket pitch on Wednesday night.
Around a dozen caravans, as well as livestock including horses and ponies, have been seen at the site.
They are occupying one of the last remaining sports fields open to the public while work continues on a £36 million regeneration project at the sports centre that is due to be complete in 18-months’ time.
READ MORE: Southampton Sports Centre travellers seen with livestock in field
In a statement, a spokesperson for the council said: “The council has visited the unauthorised encampment at Southampton Outdoor Sports Centre, and our Stronger Communities Team has completed statutory welfare checks.
“A direction to leave has been served and the police have also issued a section 61. The people who set up this unauthorised encampment have been ordered to leave the site by 2pm today (Saturday, July 26). We will continue to work with partners to resolve this situation.
“Any reports of criminality or anti-social behaviour should be reported to the police on 101 or their web-based reporting facility.
“Southampton City Council will work with partners, including the Police and the occupants of the encampment, to resolve this situation and reduce any impact on the community.”