One in 500 adult men have an undescended testicle. In contrast, almost all men have one testicle that "rides" higher than the other. It is impossible for HANSEL to tell you whether your situation is a normal case of "riding-high" or a potential fertility problem.
For normal sperm production to occur, the testes must be maintained at a temperature lower than your body temperature. If your testicle is undescended, sperm production may be reduced and/or maturation of the sperm limited, both of which lower a man's fertility.
Other factors which may cause problems of sperm production and maturation are previous infection, such as mumps; chemical and environmental factors; drugs; and a varicocele (a varicose vein in the scrotum).