Legal analysis: Although there is no written contract, card opening means the establishment of the contract, and card withdrawal means the termination of the contract. As long as there is no breach of contract, the gym has no right to unilaterally terminate the contract, so it cannot return the card.

Legal basis: Article 176 of the Civil Law of People's Republic of China (PRC) voluntarily participates in cultural and sports activities with certain risks. If the actions of other participants cause damage, the victim shall not require other participants to bear tort liability, except that other participants have intentional or gross negligence in the occurrence of damage.