If you don't sew, or if you do not possess needle and thread (of the right color), bring the shirt into a dry cleaner's shop and ask that they repair the shirt. Most can do it by hand or have a sewing machine that can stitch in the same pattern. They'll definitely have the thread in the correct color. 3rd alternative is to ask your GF.
If the shirt is not too old and rest of the shirt is in good shape I would write Nike nicely and request a repair/replacement. They're no LL Bean but you never know...
I expect the needlework on the shirt to last through its life (unless abused).
Yes, i have had something like this happen, too, right after the first few washings. it was also a cheap crappy nike polo. I fixed it with a needle and thread.