The Germany international has become one of the most sought-after talents in world football as he heads towards becoming a free agent.
Schalke have been unable to put fresh terms in place with the 22-year-old midfielder, with interest in his services steadily building across Europe.
“I have to find out for myself what the next step should be,” he told reporters following Schalke’s 2-2 draw with Cologne.
“I have to consider a million things. I am a person who is very meticulous in such decisions. I play through all the scenarios. So I need time.
“There doesn’t exist a deadline, but I think we are in the final phase.
“The final decision will be made in January.”
Goretzka is currently in his fifth season with Schalke, having joined from Bochum in 2013.
He delivered a personal best haul of eight goals across all competitions last season, before playing a leading role as Germany secured Confederations Cup glory in Russia.
A further six goals have been added to his tally in 14 appearances for club and country this term, with the uncertainty surrounding his future proving to be no distraction.
Schalke sporting director Christian Heidel had announced in November that he was still hoping to see Goretzka stay put.
He told SportBild: "I think if Schalke had no chance to keep him I would be the first to know that. But I haven't received that kind of information until now.”
Goretzka would, however, appear to be edging towards the exits, as he will be free to discuss pre-contract terms with prospective new employers from January.
As that is when he is planning to unveil his plans, he can be expected to hold talks with his many suitors before finalising a decision.