Guler 'wasn't fit to play' in Portugal defeat, Montella insists
Eyebrows were raised as Guler was forced to settle for a place on the bench, while only appearing for the final 20 minutes of his nation's loss in Dortmund, despite making such a positive impact in their opener against Georgia.
The Real Madrid prodigy scored a sublime long-range effort in the 3-1 victory, becoming the youngest player to find the net on his European Championship debut in the process.
The 19-year-old only played 10 times in LaLiga last season, with Montella believing a lack of competitive action is a concern for his players.
"Arda wasn't fit to play," the Turkiye head coach said. "I can say clearly he could not play more than 30 minutes without increasing the risk.
"There was also a temptation of not putting him 20 minutes from the end, but I finally gave in because good players must play, in my opinion.
"Because we often tend to forget that most of our footballers are not used to playing with continuity in their clubs, and I am talking about one game a week. When you play once every four days, it's another sport. You need to be physically fit, you need to be prepared.
"Arda is a great, smart guy. He is very passionate about his country, is proud of his country. But even though he knew that he was risking an injury by playing, he wanted to be on the pitch."
Despite that Portugal defeat, Turkiye are second in Group F with three points, and a draw from their final game against Czechia would be enough to secure their place in the last 16.