In a fairly obvious sense, any native speaker of a language can be said to know the grammar of his or her native language. After all, native speakers clearly know how to form and interpret words, phrases and sentences in their native language, Radford (1997). But this, clearly, is not the case with L2 learners. In today’s world, bilingualism has become an entrenched part of societal values. The pre-eminent position of the English language in global affairs has made its use widespread in international trade, international scholarship and scientific research. It is used as a second tongue to millions of users of other languages, Nigeria inclusive. However the study of psychological correlates of language has revealed that a bilingual speaker is (probably) never equally competent in both languages, Lado (1957). Therefore, this paper aims at discovering and describing the problems that the L2 learner of English will have. The theoretical frameworks adopted for the study involves a synthesis of inter language theory model and Quirk and Greenbaum’s Performance and Judgment test. The study recommends that teachers and curriculum planners should employ both diagnostic and prognostic methods in addressing problems encountered by the L2 learners of English and that language learning tasks should be made to accommodate a variety of language activities since languages, generally, are ever dynamic.