It's not going to hurt to put fungicide out other than paying for it and potentially building a resistance. That area is weak so the potential of it becoming active is obviously there. The really early warm snap we had got the grass green and growing, but this cold snap is going to slow it back down a bit. It has to grow out of the discoloring.
If it were my yard, I'd watch it, but I have instant access to whatever I need with work. If the edges start to get darker/wet looking in color (if it gets really bad the edges will almost be an orange color), or if those spots start expanding, that's when I'd put down some fungicide. It doesn't appear to be the case right now but I'm just looking at a picture. Propiconazole is pretty quick acting.
I will say this weather is going to do some weird things this year. Here in BCS we have already had multiple 140 days (daytime high+night time lows) and we may have had a 150 which is what you look for as far as yards taking off this spring. I don't think we got our first one last year until April at the earliest and it may have even been May.
