He is physically weak but mentally sound.

他身体虽弱，但思想健康。

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Otherwise, if you are weak and often fall sick physically or mentally, no matter how much money you give your parents, they will not feel truly happy.

否则如果你身体羸弱，或者终日意志消沉，哪怕你给父母再多钱，他们也不会得到真正的快乐。

youdao

He is strong physically, but weak mentally.

他身体强健，但精神虚弱。

youdao

Tennis fans will notice an important similarity between player and coach: Mr. Lendl lost his first four Grand Slam finals and was seen as mentally weak before winning his first at age 24 and then winning seven more.

WSJ: Andy Murray Tries to Crack Tennis's Inner Circle