Hǎojiǔ méi tán gāngqín le, shǒuzhǐ dōu shēngshū le.
I haven't played the piano in a long time -- my fingers are rusty.
Tips
usage
生疏 covers two related meanings: (1) rusty/out of practice with a skill, and (2) distant/unfamiliar in a relationship. Both share the idea of something that was once close or familiar fading with time.