Trouble with smelly shoes

Not exactly a laundry issue, but I thought you all might have some ideas. My 24 year old sons tennis shoes smell like cat urine. They have not been urinated on, but they sure smell like it! I washed them in the washing machine, and that removed the odor. However, 3 days later, they smell just as bad. He showers regularly, but he works in a hot kitchen washing dishes every night. Febreeze didn't help for long. Ideas?