Celtic hero John Hartson has said he has “serious concerns” over Ronny Deila’s position in an online video posted to his Twitter account.

In the 90 second clip, Hartson said he has concerns over the team’s “inability to keep clean sheets” and said the defenders have failed to take responsibility as a unit.

He also mentioned previous European clashes, where the team has failed to hold on to a lead on several occasions.

In the online clip, Hartson said: “There are serious concerns about Ronny Deila’s position and whether or not he can get through big games and hold on to tight situations.

 “This has not just gone on in the last two or three games, this has been going on now for two and a half years.”

He added: “Basically there’s big decisions to be made and made quickly.”

Ronny Deila’s position as manager has come under increasing scrutiny following Celtic’s 2-1 defeat to Aberdeen at Pittodrie.

The Herald has previously reported on rumours of Ryan Giggs taking over at the club.