Pundit Michael Stewart insists Ange Postecoglou is already coming under pressure at Celtic after early results.
The Australian secured the first competitive win of his reign against Jablonec as he looks to have guided the side to the next Europa League qualifier round.
The 4-2 victory in the Czech Republic comes after an opening day Premiership defeat to Hearts and the Champions League flop against Midtjylland.
There was also warning signs going into the clash with Dundee United on Sunday after Jablonec netted two soft goals in the first leg.
Stewart told BBC Sportsound that the defensive frailties could be a huge problem despite the additions of Carl Starfelt and Joe Hart.
He insists Postecoglou has to start picking up results or it is going to hand him an uphill battle in Glasgow's east end this term.
Stewart said: "I don't think there's any question. That is a major issue for Celtic.
"They're trying to rectify it with Starfelt and Joe Hart but it's going to take time.
"And more recruits as well, because the quality isn't at the level that they're looking for.
"They weren't great goals to concede and it's going to be something Postecoglou is concerned about.
"All he can do at the moment is muddle his way through and buy himself time.
"The Jablonec win was a positive, but if results don't improve, it just continues to heap more and more pressure and makes it more difficult for him to implement what he's trying to do and sign the players he wants."
