They arrived at the Bawtry Road facility in Tinsley earlier this week, parking caravans and vehicles on one of the car parks.
The complex is used by thousands of people every week, with students and sports teams from across South Yorkshire hiring the multi-million pound facilities for activities including football.
Sheffield Hallam University spokesperson said the sports park is open as normal.
South Yorkshire Police and Sheffield Council have been alerted.
In a statement, SHU said: "We are aware of the presence of travelers at the car park of our Sports Park on Bawtry Road.
"This is private land and we are liaising with the police and council to take the necessary action to ensure they leave in a safe and swift manner.
"Our primary concern is for the welfare and safety of our students, staff, visitors, and close neighbours.”
Travellers have set up camp illegally on the car park outside Thorncliffe Health and Leisure Centre, High Green, on a number of occasions over recent weeks.
More to follow.