Procedural memory consolidation has been shown to enhance a variety of perceptual and motor skills during sleep, but only recently has this effect been investigated in trained musicians performing music. I tested the extent to which expected music performance skill improves over a night of sleep and to what extent the new skill memory may be fragile following initial learning. Musicians (N = 60) learned a 13-note piano melody in individual evening training sessions under one of four practice conditions. Performance of the target melody was tested the next morning following a night of sleep. In line with previous research findings, subjects showed evidence of overnight gains in performance speed and accuracy. However, these results reveal, for the first time with musicians, that additional practice on a second, similar melody seems to inhibit these overnight gains, perhaps indicating that the overnight consolidation of new skill memories is susceptible to interference from similar tasks.