Turkey always have a potential to upset big teams. But the problem is, their defending isn't in good condition at the moment. We saw this clearly in the Georgia game. If there was a more capable team as an opponent, probably Turkey would lose points. Roberto Martinez also made a statement pointing this weakness. He would like to control the game for sure by overwhelming the opponent.
There is a chance that we might not see Arda Güler in the starting eleven of Turkey too. He is said to be tired. This would be an important loss of dynamism for the team. I feel like Portugal won't lose again but there might be a chance for a draw. It depends on how strong Turkey will answer in the attacking line.
And Portugal is also quite the favorite to get through the group phase and they are even favorites to win so I don't think there will be any surprises in this match.