The Spanish head coach has struggled to get the best out of his squad this season which includes the German striker who has played less than 200 minutes so far this campaign for the Hammers.
Bild has covered an interview he’s given to a German podcast and quoted him saying what a risk it was moving to London where he may never get a chance on the international stage again.
"Of course, I also had very intensive discussions about such a risky step. Because I knew that I was taking a step deeper and taking a certain risk that I wouldn’t play internationally (in Europe) next year, maybe not the year after that either, and that I would make a big, big change.
"I was aware of that, I communicated a lot with the coach, spoke a lot with Tim Steidten, who I know from my time at Bremen, which is how we got in touch so closely. Of course, we had completely different goals. Things were going really badly for me too, to put it bluntly."
On his injury, Fullkrug spoke about the disappointment in coming close to full fitness before ending up in the medical room once again in a stop-start spell of his disrupted Premier League career.
"I was injured for three months and didn’t even reach my top performance because I’ve only been training for a week and a half. It seemed like I was back at a good level relatively quickly because I came in and scored the goal.
"My Achilles tendon was inflamed and it was really annoying. I’ve had something like that before, it lasted six weeks, now it’s taken a bit longer and this phase is catastrophic. You just want to play and you feel like you’re close, but then there’s another setback."
The former Borussia Dortmund forward bagged 15 goals and 11 assists last season for the Bundesliga side in 43 appearances. This season he has just six appearances with just a single goal to his name which will be a major let down for Lopetegui who will have had the desire for a talented striker this season.