Werner and Ziyech officially become Chelsea players on July 1 but they cannot play for the Blues in the remaining games this season.
Lampard is working out a training schedule for the pair to ensure they hit the ground running at the start of next season.
“I am in the process of arranging that plan now," said the Chelsea manager.
“They are in different positions in the fact that Hakim has not played for a long time because of the Dutch league situation and Timo finished at the weekend.
“So we will formulate a plan for them that will be slightly different individually. And I will decide in the meantime how it looks at the training ground, and whether that means mixing with the squad or whether it means doing some physical work in the short-term for themselves.
“We have to make sure they will arrive at good fitness levels and freshness levels for next season. When I feel it is the right time to bring them in and around the squad this season I can do that. If not, the priority is that they are fresh and ready for next season."