FREMANTLE forward Hayden Ballantyne has not been penalised for using his phone during last Friday's NAB Challenge clash but the AFL's competition integrity department has given him an official warning.

The integrity department conducted a full investigation into Friday night's unusual incident.

Ballantyne suffered a left hamstring injury during the second quarter of Fremantle's 60-point win over Richmond in Mandurah and immediately went to the rooms for treatment.

Shortly after, the despondent small forward was caught on camera speaking on his mobile phone while the match was still being played, breaching integrity rules.

An investigation of Ballantyne's phone records confirmed that he had simply spoken to a family member following his injury.

AFL general counsel Andrew Dillon said a formal warning was the most appropriate course of action in this case.

But he echoed AFL CEO Gillon McLachlan's comments on 3AW on Monday, saying the incident served as a sharp reminder to all players and officials that the use of mobile phones in restricted areas was prohibited, and that a stronger penalty could be applied in future cases.