Drury cited Silk’s unavailability to train on Thursday evenings as the reason for his release from The Jakemans Stadium.
Speaking to bufc.co.uk, Drury said: “Gary is a top professional but he cannot train on Thursday evenings due to his university commitments — and I need all my players available for training on Thursday nights.
“That is the crucial time of the week when we work on team shape and set-pieces.
“I have nothing but respect for Gary and what he has done for the club since I have been here, but his unavailability on Thursday nights forced my hand.”
Silk (28) made 26 appearances for the Pilgrims in 2012-2013 — the last of which was against Gainsborough Trinity on February 2.
He moves on with the best wishes of everybody at Boston United.