This study contributes to the discussion about the status of the weaker language (WL) by investigating whether reduced input in Russian in a Turkish-dominant environment is sufficient for monolingual-like acquisition of the WL. It focuses on the acquisition of Russian cases by a Turkish-Russian child who has acquired his Russian in the Turkish-dominant environment mainly through interaction with his multilingual mother. The data were collected via video/audio recordings, covering the period of between two years and eleven months and four years of the participant. First, the data were examined in terms of the availability of Russian cases and their functions. Then, the study looked into whether the data were marked with deviations from monolingual norms in terms of error rates and patterns. The findings suggested that despite the reduced input, the acquisition of Russian cases by the Turkish-Russian participant follows the same pattern as monolingual acquisition does.