Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Rank | Player | Points | Points defending | Points won | New points | Withdrew due to |
| --- | --- | --- | --- | --- | --- | --- |
| 5 | Juan Martín del Potro | 5115 | 720 | 0 | 4395 | right wrist surgery |
| 6 | Nikolay Davydenko | 5145 | 360 | 0 | 4785 | broken wrist |
| 20 | Radek Štěpánek | 1705 | 90 | 0 | 1615 | fatigue |
| 23 | Tommy Haas | 1660 | 180 | 0 | 1480 | right hip surgery |
| 32 | Gilles Simon | 1395 | 90 | 0 | 1305 | right knee injury |
| 36 | Ivo Karlović | 1295 | 10 | 0 | 1285 | right foot injury |
| 10 | Kim Clijsters | 3890 | 0 | 0 | 3890 | left foot injury |
Question:
did gilles simon withdraw because of a right or left knee injury?
Answer:
right