There are 2 important aspects to any young talent making the grade at the highest level. Talent and a very resilient psychological personality.
I have seen the talent in Sancho, but I have also seen on the pitch behaviour I do not like. How anyone can support the behaviour of a 17 yr old going on strike just before the season begins i do not know.
It is nothing to do with "chances" in the first team .
Let him go and wish him good luck
He will regret it one day.