From Longman Dictionary of Contemporary Englishnot have a prayer (of doing something)not have a prayer (of doing something)informalCHANCE/OPPORTUNITY to have no chance of succeeding He tried hard, but he didn’t have a prayer. They don’t have a prayer of winning. → prayer
Examples from the Corpus
not have a prayer (of doing something)• Boxing White Hopes like Cooney do not have a prayer of toppling Tyson.• The Seahawks don't have a prayer of winning the Superbowl. 