The loanee suffered the issue while playing for Hibernian in Scotland, during a game against Elgin City in January.
But he has recovered well in that time.
The 31-year-old has now resumed light training after a specialist gave him the all clear.
His manager Paul Heckingbottom spoke about the situation.
"We had him in the squad when we came in as he returned from concussion but then he didn't feel right," he said to reporters.
"He wasn't happy. He was still having the symptoms.
"You cannot be too careful with a head injury but Adam has been to see a specialist who was happy while the scans came back clear.
"We've also been working closely with Liverpool and now Adam is doing low-key training and, although we haven't set any sort of timescale on his return, we hope to have him out working on the grass soon."