“Motherwell opened old wounds,” the former Celtic striker has written. “Limp, lazy, leaderless. This team lack character, knowledge and more importantly knowhow.
“So Peter will be asking himself how can I continue trusting Ronny? If Ronny is in control of transfers?
“Do I trust Ronny to bring new players to the club in January after his current track record? Simply, have we progressed under Ronny?”
Celtic’s performances and results have been disappointing in recent weeks, and manager Deila has come under pressure.
The Bhoys, who failed to progress to the group stage of the Champions League at the start of the season, could not qualify for the knockout rounds of the Europa League.
Last weekend, the Hoops suffered a surprise 2-1 defeat to Motherwell at Celtic Park.
Celtic are still favourites to win the Scottish Premiership title this season, but the Glasgow giants are now level on points with second-placed Aberdeen.
The Bhoys, though, have two games in hand, but given their current form, there is no guarantee that they will pick up maximum points from those fixtures.
Celtic will return to league action on Sunday afternoon when they take on Hearts away from home at the Tynecastle Stadium in Edinburgh.