Sanogo did not make a single first-team appearance for Arsenal this season with Arsenal boss Arsene Wenger saying the medical problem was "confidential".
And Wenger added the injury was in his calf but not a life-threatening problem.
Sanogo returned to action in April and scored a hat-trick for the under-23s against Reading but he has not been offered a new deal by the Gunners.
Speaking to French newspaper L'Equipe, Sanogo spoke about his injury woe and why his career at Arsenal faltered.
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It was very hard when I was injured. You feel so mentally alone.
He said: "My left calf is healed. It kept me off the pitch for nearly 7 months. I came back in January, with a fitness trainer. I was able to play again for the Arsenal reserves.
"Three games with four goals. It is not a lot, but it was a real source of relief for me.
"It was very hard when I was injured. You feel so mentally alone.
Yaya Sanogo will leave Arsenal at the end of the month
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"There is virtually nobody at your side. And there is this frustration about not knowing what the source of my pain was.
"The injuries stunted my progress, there were moments where I was good. I remember the summer of 2014 when, during the Emirates Cup, I scored a quadruple against Benfica.
"And then there were some bad decisions, and I maybe did not always do what was necessary to impose myself."