Apple leaf issue - please help

Hi, I am new to apples. Found one leaf that looks really not good on my first small apple tree. Can’t identify it using Google. Any ideas?

Could be any number of things: Heat, drought, fertilizer burn… This time of yr leaf issues happen but aren’t important unless it’s most of the leaves or increasing rapidly.

Thanks! I was concerned because it is my only and well cared tree planted this spring - I didn’t fertilized it yet, water regularly. But weather is very strange this year, was almost record hot, so may be this is the reason. I just wanted to make sure it is not a symptom I have to correct right away before it affected whole tree. .