Henderson has been expected to leave Manchester United this summer, but the Red Devils wanted to make sure they secured a replacement first.
They are set to sign Fenerbahce goalkeeper Altay Bayindir to provide cover for number 1 Andre Onana and release Henderson to go.
Henderson will be severing his ties with Manchester United permanently when the move goes through.
And Crystal Palace will put the goalkeeper through his medical checks on Sunday.
Henderson spent last season on loan at Nottingham Forest and the Tricky Trees were keen to bring him back this summer.
The goalkeeper has made a total of 29 appearances for Manchester United, keeping 13 clean sheets.
He was on the bench for the Red Devils’ 3-2 win over his former club Nottingham Forest in the Premier League on Saturday.
