Just speak to the student, 1 on 1 quietly somewhere where there is no one around. Start by bringing up the conversation "Hey I noticed you speak and listen really well, and thats amazing (bring up the strengths of the student), but you seem to struggle in writing and reading a lot more than you should have, and that is fine, but it might be due to a condition known as ...."
And then suggest the course of action. Firstly, I have to applaud the teacher for at least being able to identify the situation and the potential cause, this can go a long way for helping the student. Just kindly suggest a visit to the doctor, after all there is no harm. If the student has no family members around him/her, then it would be great that someone follows the student to the doctor, since it was mentioned he/she struggles in reading and writing.
The teacher can also look online for possible Dyslexia tests, I am not sure how accurate those are but it could help in clearing the situation or give us a better judgement.
We do not want the student to be feared of the doctor or a potential Dyslexia condition, it is important the teacher tries to phrase it in a manner when speaking to the student that it is better for him/her to visit the doctor, just to find out so we can help the student. Whatever the outcome is, we should just accept it and make the best out of it.