The 34-year old Dutch striker went down with a ruptured ACL last July and according to head coach Ryan Nelsen, could be back in action within a month.
"Obviously, it is extremely exciting," Nelsen told MLSsoccer.com. "I think you can look at him there [on the training pitch] and you can see some of the finishing that he does.
"He is a long way off in terms of match fitness and that is why we are trying to get him into these 4-v-4 and 5-v-5 games, to get guys around him and to get his feet moving quicker and get that football fitness up.
"The more we can do that with him, then the quicker we can potentially bring him back. But we aren't going to bring him back until he is really ready because he has been out for a long time now and it wouldn't do him justice."