The rupture comes after Ukrainian authorities on Monday (11 November) charged Serhiy Vlasenko, the lawyer of jailed former PM Yulia Tymoshenko, with domestic violence in a case which could see him also jailed for three years.
The move came 48 hours before a European Parliament mission on Wednesday in Brussels gives a final verdict on whether Ukraine has stopped "selective justice."
It also came one week before EU foreign ministers next Monday decide whether to sign the pact at an EU summit with former Soviet states in the Lithuanian capital on 27 November.
Speaking to EUobserver from Kiev on Wednesday, Vlasenko said: "They activated my case as another bright example of selective justice."
He said they did it as a PR stunt to force the EU parliament to give a negative verdict, helping Ukrainian President Viktor Yanukovych to blame the Vilnius failure on the EU.
"I have no doubt in my mind Yanukovych has decided not to sign the treaty … But this enables him to say: 'Look. I did all my homework. I adopted a lot of pro-EU laws, except in the area of politically motivated cases. Now you should sign because of the Russian pressure on my country'."
An EU diplomat, who asked not to be named, gave the same opinion.
"We are sure the signature won't happen," he said.
"The Vlasenko case is designed to influence the EU parliament report. In this way, they are trying to provoke the EU to fire the first shot in the blame game of who is guilty for the non-signature."
He added that Yanukovych will probably come to Vilnius to sign some minor agreements, such as a common aviation space with the EU, allowing cheap flights between European and Ukrainian cities, in order to keep EU relations ticking over.
He noted that Yanukovych is unlikely to join Russia's Customs Union either.
With the status quo helping the President's clan to stay in control of Ukrainian business and to retain power in upcoming presidential elections without interference from Brussels or Moscow, the EU diplomat added:
"They want to keep both Russia and the EU at arm's length for as long as possible."
The Vlasenko blow comes as no surprise to EU negotiators.
The Ukrainian parliament is due to hold an extraordinary session at 10:00am Kiev time on Wednesday to decide whether to let Tymoshenko go to Germany for medical treatment.
But relevant committees have not even drafted the bill which might see a positive outcome.
Vlasenko noted that Ukrainian prosecutors are at the same time preparing material to prosecute the ex-PM in fresh cases on alleged embezzlement and on alleged involvement in a 1990s contract killing.
Vlasenko spoke to this website after being released on bail.
But he said his bail conditions are so severe he could end up in pre-trial detention at any moment.
He is charged with hitting his ex-wife, Natalya Okunska, in the face five times when she she visited his flat one evening in 2008, causing bruises.
He denies having ever hit her.
He said witnesses saw her leaving his home on the night in question with no marks on her face and with no signs of distress.
"The administration is controlling all of her statements. She has access to the main TV channels and to all the top people in government," he noted.
He said that when he was summoned to the prosecutor's office on Tuesday, Okunska appeared on the scene, surrounded by TV cameras, in an attempt to "incite" him to make a show of anger.
He also noted the former model is now running for parliament in a disputed seat related to flawed parliamentary elections last year.
Vlasenko said there is "a one percent chance" his case is an attempt by Ukraine to extract last-minute concessions from the EU, for instance, on trade tariffs.
He added it would be "a miracle" if the parliament found a way to free Tymoshenko at Wednesday's session.
The EU diplomat used the same vocabulary.
"It would be a miracle if parliament adopted the law, as well as two other ones which are important for the EU: on the independence of the prosecutor's office and on electoral reforms," he said.
The diplomat noted that senior EU figures, such as Lithuanian President Dalia Grybauskaite and Polish foreign minister Radek Sikorski, have "changed their rhetoric" in recent days.
The previous EU message was that if Ukraine does not sign the treaty in Vilnius it will lapse, once and for all, into Russia's sphere of influence.
But the latest statements say it would not be a disaster if the treaty is signed later down the line.