We do not know if you have noticed, but to make it clear from the beginning: Cristiano Ronaldo generally, not to mention in all cases, wears long sleeves; as here,

or here,

in another case,

ok we spend this,

the last one.

There are 2 possibilities for such a choice: Or Ronaldo will create its own style, be easily visible on the pitch (as needed) or superstitious. Since we can not prove the first, let's deal with the second.

In important championships such as Euro 2004, the 2006 World Cup and Euro 2012, Cristiano Ronaldo was wearing a short sleeve shirt, which brought nothing but tears on the field.

While the opposite of Euro 2016, where not only went to the final but Portugal was declared European Champion.

If that is the real reason, Ronaldo has to change his strategy that this time it came out bad.