Robben underwent treatment in the Netherlands and joined the team in Johannesburg last Saturday but had been training on his own until Friday.
"This was his first complete training since we got together and that is something, " coach Bert van Marwijk told a news conference at the Moses Mabhida Stadium in Durban.
"Now we have to wait to see how his hamstring reacts tomorrow morning but in normal circumstances he would not play against Japan."
"They have been searching for a tactical style that would suit them and played many friendlies which they lost," Van Marwijk added.
"But they seemed to have found it and you always have to be ready when the tournament starts and that is exactly what they were."
"It is rather warm today and the forecast for tomorrow is that it will be even warmer, but we just have to deal with that," he added.
"It is a fast ball but after working with it you get used to it. But now we are playing on sea level and then it reacts normally," said the more positive Dirk Kuyt who scored the second Dutch goal against Denmark.
