Barry McIntosh spoke of his anger at Newcastle's wage offer for the 26-year-old, which is thought to be around £40,000-a-week - less than he currently earns in Germany.
"As it stands there is not a hope in hell that he will be going to Newcastle. In fact I am angry at their attempts to do it, and behind my back also," he told Sky Sports News.
"They have made an approach, but their offer equates to somewhere in the region of £40,000-a-week - which is just ridiculous.
"Why on earth would Tranquilo move to Newcastle for less money? No offence to Newcastle, he would possibly consider going to Arsenal, Liverpool even Tottenham for less - but not Newcastle."
Swiss international Barnetta has made 59 appearances for his country, scoring 8 goals.
Magpies' Boss Alan Pardew reacted angrily McIntosh's comments, saying: "I'm not going to answer that particular agent - it's not an agent I know or have ever spoken to.
"For anybody to say £40,000 per week is a derisory offer is absolutely astonishing."