Celtic are lying at the bottom of Group F of the Champions League and have just one point from their four group games.
The Scottish champions need results in their last two games to have any hope of finishing third and playing in the Europa League in the latter half of the season.
Celtic’s performances in the Champions League have come under scrutiny, but Hartson believes that they have played well in most of the games in Europe this season thus far.
He stressed that the issue has been scoring goals in the Champions League and they have just not been clinical enough inside the penalty box, which has not been a problem domestically.
Hartson said on the Go Radio Football Show: “Domestically, they are scoring goals for fun but when it comes to the Champions League, they have just not been clinical enough.
“They have actually had a very good Champions League but they haven’t taken their chances.
“Goals win you games and that’s exactly what you have to do.”
Celtic will be desperate for a win when Shakhtar Donetsk visit Parkhead next week in the Champions League.
