MYSTERY surrounds the fitness of out-of-contract midfielders Josh Kelly and Jacob Hopper after the pair was injured at training on Saturday.

A Giants spokesman told AFL.com.au on Sunday afternoon that the midfield duo would be further assessed in the coming days.

However, the spokesman would not reveal the exact nature of their injuries.

Kelly, 22, who is out of contract at season's end and has attracted enormous interest from rival clubs, has featured in every game this season, averaging 29 disposals.

Hopper, 20, has lined up in six matches for the Giants this year and is also unsigned beyond 2017.

Hopper has not played since having surgery to repair a broken finger he suffered against St Kilda in round seven, and was due to return soon after the bye.

The Giants had their mid-season bye this week and face the Brisbane Lions at the Gabba next Saturday.