Contrary to the long-standing view that regards fixedness as one of the defining features of phraseological units (PUs), investigation of authentic texts suggests that PUs display a higher degree of variability than was generally assumed. The present paper aims to classify and provide explanations for the types of lexical variation in Modern Arabic PUs that have been calqued from English. It shows that calqued PUs display types of lexical variation that are different from those displayed by original PUs. The study also argues that explanations that are restricted to only one branch of linguistics cannot fully account for the types of variation found in Arabic calqued PUs and that an approach that combines both linguistic and extra-linguistic aspects can provide a more appropriate explanatory tool for such variation.