The NRL is investigating the appearance of suspended Cronulla coach Shane Flanagan's at a Sharks trial match on Saturday night.

Flanagan's attendance at the match at Shark Park would appear to be a breach of the 12-month suspension handed down by the NRL in December relating to governance issues at the Sharks in 2011.

The NRL is seeking a written explanation from both Flanagan and the Sharks to assess whether it was a violation of his suspension.

Flanagan, who watched the 28-22 loss to the Tigers from a corporate box on Saturday night, is appealing the ban.