Christian is trying to build up his fitness in order to find a new club.
The 29-year-old began his senior career at the Dutch side, spending five years there before joining Spurs.
John Heitinga is the manager of the club's reserve team.
After his contract with Inter Milan was terminated last month, he has been linked with a return to the top flight.
Doctors gave the green light to resume his career last month after he suffered a cardiac arrest while playing for his country at the European Championships.
Italian regulations prevent athletes with an ICD from playing professional sport in Italy, leading Inter to agree to release him.
I'm very happy to be here. It feels like coming home to me because I was here for so long.
I can train with a group. That is the right foundation for me. When I find a new club, I want to perform well there as quickly as possible.