John Mjallby says Celtic must tighten up at the back against Udinese but has backed his defenders to come good in Thursday's Europa League game.
Celtic's defence looked shaky despite keeping a clean sheet in Saturday's 2-0 win over Inverness Caley Thistle.
"We can't make mistakes like we did on Saturday when we play Udinese," said Celtic assistant manager Mjallby.
"We just need to show a little more leadership and not make silly mistakes, but we have good experience there."
Mjallby found it difficult to exlain the uncertainty at the back this season.
"Last season, we shouldn't forget that we had the best defensive record in the league despite being a very attack-minded team," he said.
"So it is a bit of a surprise that this season we have not played as well as last season.
"Maybe because of injuries, we have not been able to get a settled back four, or back two in the centre."
Mjallby realises that Celtic, who lost their opening game away to Atletico Madrid, have a difficult task qualifying from Group I but is hopeful that they can improve their recent European form.
"It is probably between Udinese and Atletico Madrid, with Rennes just behind," the Swede said when asked who are favourites to top the section.
"We have three very hard teams to play against, but it will be a great experience for all of the players.
"It is a great game on Thursday - high quality opposition. They have been very impressive at the start of the league over in Italy.
"If we want to get through, it is very important game for us to try to get a win and three points.
"We have only played one game. If we get a good result on Thursday, we are definitely back in it."
Mjallby is sure that his side are capable of beating the Italian side.
"I don't think you can go into a game and think you are not going to get a result - and a result is a win, especially when you are playing at home," he said.
"We need to be solid but not frightened to go forward."
Mjallby recognises the threat of 33-year-old Italy forward Antonio Di Natale, who gave Arsenal's defence a hard time despite the English side winning their Champions League qualifier.
"He has been scoring goals for years," added the Celtic assistant. "He has such clever movement and is deadly when it comes to dead-ball situations.
"We definitely have to make sure that all the defenders are wary of him and that he does not get enough space."