I'll take a day off today because of poor health. Could you tell this to the Manager?
I'll take a day off today due to bad health. Could you let the Manager know this?
I'll be on sick leave today. Please tell it to the Manager.
『休む』はtake a day off.
体調不良は poor health (bad health)
あるいは、be on sick leaveで体調不良で休む(休んでいる)となります。
伝えるは、tellでよいでしょう。あるいは、let 人 know など
ちなみに午前休/午後休は
morning off・afternoon off といいます。
I'll take a morning off tomorrow.
(明日は午前休を頂きます)
I'll take tomorrow morning off.
(明日の午前中は休みを取ります)