后患无穷

it will cause no end of trouble (idiom)

empress / queen / (archaic) monarch / ruler

back / behind / rear / afterwards / after / later / post-

to suffer (from illness) / to contract (a disease) / misfortune / trouble / danger / worry

not to have / no / none / not / to lack / un- / -less

endless / boundless / inexhaustible

poor / destitute / to use up / to exhaust / thoroughly / extremely / (coll.) persistently and pointlessly

if you beat the snake without killing it, endless evils will ensue (idiom)