Players union FIFPro says Luis Suarez's four-month ban "from all football-related activity" for biting Italy's Giorgio Chiellini "lacks clarity," Simon Stone of BBC Sport reports.
The 27-year-old Uruguay and Liverpool striker was also banned for nine international matches. FIFPro argues that FIFA has not defined what entails "football-related activities."
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Football's world governing body Fifa has refused BBC Sport's requests to explain the details of the ban.
It did, however, confirm that under the terms of the ban, Suarez, who is also banned for nine international matches, cannot train with his club and is prohibited from entering the confines of any stadium during his suspension.
"We agree that the sanction lacks clarity," said a FIFPro spokesman.
"The concept of being banned from all football-related activities is not defined."
FIFPro previously questioned the severity of Suarez's ban.
- Sarah Barshop