A.T. Robertson Commentary 1 Corinthians 15:27

"For, He put all things in subjection under his feet. But when he saith, All things are put in subjection, it is evident that he is excepted who did subject all things unto him." — 1 Corinthians 15:27 (ASV)

He put (υπεταξεν). First aorist active of υποτασσω, to subject. Supply God (θεος) as subject (Psalms 8:7). See Heb 2:5-9 for similar use. Cf. Psalms 8.

But when he saith (οταν δε ειπη). Here Christ must be supplied as the subject if the reference is to his future and final triumph. The syntax more naturally calls for God as the subject as before. Either way makes sense. But there is no need to take ειπη (second aorist active subjunctive) as a futurum exactum, merely "whenever he shall say."

Are put in subjection (υποτετακτα). Perfect passive indicative, state of completion, final triumph.

It is evident that (δηλον οτ). Supply εστιν (is) before οτ.

He is excepted who did subject (εκτος του υποταξαντος). "Except the one (God) who did subject (articular aorist active participle) the all things to him (Christ)."