Maguire's statement said: "Because of repeated press speculation about my situation at Jackdaws Castle, I have asked Colin Smith if he will release me from my retainer at the yard. After much discussion he has agreed and I will become a free agent with immediate effect.
"However, I will not be leaving Jackdaws Castle and I would hope that I would continue to ride for the majority of the owners who have so far been very supportive, subject to the wishes of David Nicholson.
"I very much regret having had to take this action, having had the support of David Nicholson and Colin Smith, but this seems to be the only way of clearing the air, stopping the speculation and not having all my rides under a press microscope."
Maguire's position as number one at the yard had come under threat in recent weeks when some of the stable's owners expressed a preference for their horses to be ridden by Richard Johnson.
Johnson partnered Darren Mercer's Escartefigue into second place behind Teeton Mill in Saturday's King George VI Chase, while Maguire was aboard the outsider Mulligan, who was pulled up. However Nicholson insisted that Maguire remained the stable's first-choice rider.
After last night's decision by Maguire, Nicholson said: "I am not prepared to say anything tonight but will be issuing a statement tomorrow."
Jackdaws Castle is a state-of-the-art training establishment, owned by Smith's company, Ford Farm Racing, where Nicholson is a salaried employee.
Speaking on Monday, Smith said: "If Adrian jacks it in as stable jockey at the yard in the next few days over what's been happening - and I don't blame him if he does - there will be no retained jockey at the yard for the rest of this season and possibly next season as well."
Maguire's career has been blighted by a series of misfortunes that have seen him spend lengthy periods on the sidelines and have prevented him from becoming champion jockey. He has missed three of the last four Cheltenham Festivals.