Russian investigators refused to allow jailed U.S. investor Michael Calvey to remove his electronic ankle bracelet in order to undergo an MRI scan required for cancer treatment, the Financial Times reported Thursday. 

Lawyers for Calvey, who was detained last February on embezzlement charges that he says are being used to pressure him in a business dispute, revealed in June that he had a malignant tumor in his leg. While the court allowed him to seek treatment at a private hospital, his appeal for an early house arrest release was rejected.

In the absence of MRI results, doctors were forced to remove the tumor using an outdated method that required Calvey to undergo an additional round of radiation therapy, the FT reported, citing unnamed sources. 

Calvey’s cancer is reportedly in remission following the treatment. 

The investor was detained alongside five other executives of Russia’s largest foreign-funded equity group Baring Vostok on accusations of embezzling 2.5 billion rubles ($36.4 million).

The case, which the defendants say is an attempt to pressure them in a business dispute over control of mid-sized bank Vostochny, has rattled Russia’s business and foreign investment communities.

According to information obtained by the Financial Times, backchannel efforts to lobby Kremlin officials and security forces to reduce the charges against the defendants have stalled in recent weeks, leaving little hope for Calvey’s early release.