South Africa and FC Porto striker Benni McCarthy is in doubt for Tuesday's European Champions League away match against Scottish side Rangers.
Benni McCarthy in action for South Africa before his new hairstyle
McCarthy was dropped at the last minute for a weekend Portuguese league game for disciplinary reasons.
Coach Co Adriaanse ordered the South African to sit out the team's match on Saturday against Rio Ave reportedly because the 27-year-old appeared at a training session wearing new hair extensions.
The Dutchman barred players from wearing earrings or "unusual" hairstyles shortly after he took charge of the club in May.
"A rule of the disciplinary code was broken," Adriaanse told sports daily A Bola without confirming if the violated rule related to the player's hairstyle.
"It wasn't a difficult decision. This team has rules which apply to all its professionals. Even the best and the most expensive players have to respect them," he added.
"I am going to think first before I decide if I will call on him for the match against Glasgow Rangers," Adriaanse said.
McCarthy, Porto's top scorer for the past two seasons, was replaced by Bruno Alves against Rio Ave.
The former European champions scored three goals in the last four minutes of Saturday's match to top Rio Ave 3-0.