Adelaide United may be without midfielder Marcos Flores for Saturday evening's away clash with North Queensland Fury.

The 24-year old Argentine playmaker is in doubt after failing to complete the Reds' training session because of a hamstring complaint.

Flores appeared to sustain the injury during the session but it is too early to tell just how serious the damage is.

If he misses, it will be a big blow to the Reds as he was a key element of their 3-2 win over Melbourne Heart last Friday.