off chance
A slight, remote, or unlikely possibility. The washing machine is probably busted, but there's an off chance I might be able to fix what's wrong with it. I don't think Jack would go on a date with me, but on the off chance that he says yes, I'm going to ask him anyway!
off chance
slight possibility. I need your phone number on the off chance I need more help. There's an off chance that we might be hiring next month.