Raynor was named as the Pilgrims' number two a month ago when now-director of football, Jim Rodwell, took the manager's mantle.
Redfearn (38) said he felt he had no other option but to walk away as a Boston player.
"The club recently put out an announcement saying I should return.
"But this is not possible due to their conduct towards me.
"Boston terminated my contract as assistant manager without any notice and I cannot, under those circumstances, return.
"I am very disappointed matters have reached this stage and I have no alternative but to terminate all association with the Pilgrims."
Redfearn's lawyer Mel Stein, who represented ex-England star Paul Gascoigne at the height of his fame in the 1990s, contacted the Echo from Miami airport to offer his take on the situation.
"This has been a very difficult decision for Neil," said Stein.
Redfearn is top scorer this season with seven goals from 26 appearances, but feels his position is untenable after friend Neil Thompson was sacked as manager last month.