Police said two men, aged 18 and 19, have been arrested in connection with the attack and were being held in custody.
Officers were called to reports of an injured man in Calder Holmes Park shortly after 5.30pm yesterday (Saturday) and discovered he had suffered a single stab wound to the chest.
An air ambulance was summoned to take the victim to Leeds General Infirmary for treatment.
Detective Inspector Vicky Lawrance, said: “I’m sure that this incident will cause some concern in the local community but I would like to reassure people that swift action has been taken, with two men in custody and extensive enquiries ongoing.
“This offence has taken place in a public park during the late afternoon when there will have been a number of people around. I would urge anyone who saw any part of this incident or with any information which could help our investigation to please get in contact.”
Anyone with any information that may help West Yorkshire Police with their enquiries is asked to contact the force via 101. Alternatively, information can be given anonymously to independent charity Crimestoppers on 0800 555 111.