He suffered a gash in a League Cup tie that became infected and required hospital monitoring.
His performances on his return were not impressive, and it led to mental struggles for Keane.
"I didn't want to go out, didn't want to see anyone," Keane said in an interview with BBC Sport.
"I felt a bit embarrassed with how things were going on the pitch so I didn't want to be seen anywhere, didn't want to do anything.
"I was keeping it in for a long time, working hard, turning things around on the football pitch but in the end it sort of got on top of me. I ended up not having a full breakdown, but I was basically in tears telling my family how I felt.
"That was a big breakthrough moment where I sort of got to my 'rock bottom'. From there on I've got better and better with the help of my family and my friends and I started speaking to a sports psychologist which I still do now regularly to just keep on top of it."