The three farmers, PP Mare, Chris Naude and Johannes van Zyl, were being held in the Gravelotte police cells, Beeld reported on Thursday.
Their lawyer Aldo Rech told the newspaper they were tipped-off earlier in the week that poachers would target the area.
They reportedly claimed they gave chase to two suspected poachers on Wednesday. One of them got away, but they caught the other one, who was injured while running through dense, thorny undergrowth, and found rhino dehorning tools.
According to Beeld, they tied him up and called police to arrest him.
Colonel Ronel Otto told the newspaper police found the man with a head wound, and decided to charge the farmers with attempted murder. He had since been admitted to hospital.
Rech reportedly denied that the farmers had assaulted him.
The farmers were expected to appear in the Phalaborwa Magistrate's Court later on Thursday.