Sinnott made his name during a successful spell at Farsley Celtic
Bradford Park Avenue have parted company with manager Lee Sinnott by mutual consent, and replaced him with assistant John Deacy.
Sinnott had only been in charge since January but Monday's FA Cup exit to Buxton and poor Unibond Premier Division form have ended his spell.
Chief executive Bob Blackburn told BBC Radio Leeds: "The results have not been as either Lee or the board wished.
"The defining moment was Monday night's defeat to Buxton."
Avenue just missed out on the play-offs last season but heavy player recruitment saw Avenue tipped by many as favourites for the title.
When you've put in as much money as our board have, you need an instant fix really and second fiddle is no good
Chief executive Bob Blackburn
However, poor league form has seen Avenue slip to 16th in the table and the chance of a high-profile money-spinning run in the FA Cup was brought to an end in the dying minutes of Monday night's third qualifying round replay at home to Buxton.
It was a defeat that ultimately led to his departure.
"Obviously we've had a string of poor results to the season so far. We've heard, I wouldn't say excuses, but for want of a better word, answers, that the team needs time to gel and injury problems," Blackburn said.
"When you've put in as much money as our board have, you need an instant fix really and second fiddle is no good at Bradford I'm afraid."
Sinnott made his name in management after a successful spell at Farsley Celtic, taking them from the Unibond North to the Blue Square Premier.
A move to Port Vale followed in November 2007 but his success did not continue - he was unable to save the club from relegation to League Two and was sacked in September 2008.
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