According to the Bahrain Mirror on Sunday, Rajab had been sent to solitary confinement by the ruling regime just two days after being operated on.
The Bahrain Center for Human Rights has noted that the activist was not even given basic hygiene products after surgery.
A member of his family stressed that Rajab also required special medical attention due to the nature of his operation.
On Thursday, his relatives reported that they had been prevented from visiting him after he underwent surgery.
Rajab is being held in detention, pending trial on alleged charges of insulting the Bahraini ruling dynasty. Rajab has been arrested multiple times in recent years over anti-regime protests in Bahrain. The activist was pardoned for health reasons in 2015 before being rearrested in June 2016. He is currently on trial for tweets and statements deemed insulting to Manama and Riyadh regimes.
Bahrain has been the scene of almost daily demonstrations against the Al Khalifa rule since mid-February 2011, when a popular uprising began in the tiny Persian Gulf country.
Protesters are demanding that the ruling dynasty relinquish power and allow a just system representing all Bahrainis to be established.
The regime in Manama has spared no effort to clamp down on dissidents and rights activists. Scores of people have lost their lives and thousands of others have ended behind bars during the suppression campaign.