To express (just) in case in French, you use the expression (juste) au cas où.
Look at the following examples:
The delicate point here is the question of the mood following au cas où. Indeed, as it expresses an uncertain state or an hypothesis, you could be tempted to use Le Subjonctif. That would be a mistake!
With the expression (juste) au cas où, you can only use Le Conditionnel.