The fire was thought to have been deliberately started just before 7.30pm last night in the seating area near to the running track, before spreading to the main building.
Hundreds of children were in the building at the time but were led to safety as three fire crews were able to bring the blaze under control.
Coun Jacquie Speight, Wakefield Council’s cabinet member for culture, leisure and sport, said: “I would like to thank the staff at the stadium and the emergency services for their quick response to the incident, to ensure that everyone was evacuated safely and quickly.
“Unfortunately, due to the damage caused, Thornes Park Stadium will remain closed while investigations take place.
"This is expected to take around one week to complete. Once we have more information about the extent of the damage and repairs that are needed, we will be able to give a clearer indication of when we hope to reopen.”
Wakefield Council says it will be contacting the clubs and groups that use the facilities to help organise alternative provision where possible.
Those with Aspire memberships will still be able to use all the facilities at other leisure centres in the district at Sun Lane, Normanton, Featherstone, Pontefract and Minsthorpe.
Coun Speight added: “We really do apologise for any inconvenience caused when the stadium is closed, whilst we make the necessary repairs and checks to ensure the building is safe to reopen. We do hope that people will make use of our other facilities.
“Anyone with any information about the fire, or who saw anything suspicious around Thornes Park yesterday, is asked to contact West Yorkshire Police on 101.”