The tenacious midfielder is a player reborn under Brendan Rodgers at Celtic.
Manchester City could move for the Norwegian, who is managed by ex-Celtic boss Deila at Valerenga, this summer.
Celtic are one of the most historic sides in European football, so failing to qualify for the Champions League doesn't look good on the CV.
Ronny Deila parted company with Celtic at the end of the 2015-16 season.
Celtic secured yet another win in the Scottish Premiership at Rugby Park on Friday night.
Celtic have made a flying start to life under Brendan Rodgers.
Brendan Rodgers was appointed the Celtic manager in the summer following the departure of Ronny Deila.
Rangers boss Mark Warburton is in danger of ending up like the Norwegian at Ibrox, explains the former Celtic striker.
Rodgers replaced Deila at the club this summer after the Norwegian decided to depart.
Walker believes Celtic’s loss to Rangers in the Scottish Cup last season resulted in the club hierarchy replacing Deila with Rodgers.