。
Don't push yourself.
Literal
Impossible [object-を] do-not [so-that-ように].
無理をする ('to push oneself, to overdo it') is a set phrase. ~ないように is the negative purpose/command form — 'so that (you) don't.' The sentence trails off without a main verb; this ellipsis is a common soft-command form: 'please, so as not to push yourself.'