The 23-year-old has not managed a minute of competitive football since suffering a back injury in Germany's friendly match with Paraguay in August of last year.
The Borussia Dortmund star watched from the sidelines as Joachim Low's side lifted the world title in July following their win over Argentina, and he concedes it was painful to have missed out on the tournament.
"On one hand, it was incredible for those guys. On the other, it was personally bad situation. You know what you could possibly have been doing, possibly been called a world champion," he told Bild.
"In such stupid ways are dreams shattered. Dreams you had as a child are broken - at least, for now."
Gundogan said in the spring his target was to return to action in the early part of the new Bundesliga season, but he claims it would be unwise to set a date for his recovery as he continues light fitness work during pre-season.
"It would be irresponsible to mention a date. Of course I am eager to get back into training. After the operation, we said I hoped to be back playing again in the autumn," he continued.
"I haven't thought about a break in my career. Of course, I wondered if I would ever get back to the form I was in."
The midfielder, who scored in the Champions League final in 2013, also plans to discuss a possible new deal with Dortmund after signing an extension back in April.
"The [previous] contract was only for a year and a half. BVB wanted certainty, so as soon as I'm fit and well, we will sit down and talk about another extension and the future," he added.