Kelly out of Under-21 squad
Kelly played the full match for Liverpool against Chelsea on Sunday in the Barclays Premier League but sustained a knock during the game.
The Football Association confirmed Kelly's withdrawal on Monday morning, ahead of the team's departure for the clash in Empoli.
While Walker was promoted to the senior squad for Wednesday's international in Denmark, the other five have been lost to injury.
Leeds captain Jonny Howson was called into the squad for the first time as a replacement, and has been joined by Chelsea's Josh McEachran, Barnsley's Kieran Tripper, Leicester loanee Kyle Naughton and Crystal Palace forward James Vaughan.
Liverpool's head of sports medicine and sports science Dr Peter Brukner said Kelly was feeling the after-effects of a tough encounter at Stamford Bridge.
"Martin suffered a sprained ankle during yesterday's (Sunday's) game," Dr Brukner told liverpoolfc.tv.
"He was treated at half-time and able to continue but it was very sore after the game."
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