To determine the percentage of free throws the player missed, we first need to find out how many free throws he missed.
The player made 5 out of 6 free throws, so he missed:
\[ 6 - 5 = 1 \text{ missed free throw} \]
Next, we calculate the percentage of missed free throws:
\[ \text{Percentage missed} = \left( \frac{\text{missed free throws}}{\text{total free throws}} \right) \times 100 \]
Substituting the values we have:
\[ \text{Percentage missed} = \left( \frac{1}{6} \right) \times 100 \approx 16.67% \]
Thus, the percentage of free throws he missed is approximately 16.67%, which can be expressed as:
\[ 16.66\overline{6}% \]
Therefore, the correct response is:
16.66̅%