Giakoumakis and Furuhashi have a combined ten goals in the Scottish Premiership this season but they have failed to get off the mark in the Champions League.
Against RB Leipzig this week, Furuhashi started and Giakoumakis came off the bench, but both drew blanks as Celtic lost 2-0.
Hartson thinks it is time for the strike duo to face themselves in the mirror and hold their hands up for their disappointing performances.
The Celtic legend stressed there is no effort in raking in the praise, but when a striker misses opportunities like they did in their Champions League games, Giakoumakis and Furuhashi need to own up.
Speaking on the Go Radio Football Show, Hartson said: “They are now going to have to be disappointed with their own attempts and not taking Celtic to that next level in terms of missing their opportunities.
“They will have to have a look at themselves and say we have to hold our hands up.
“I know it’s a team game and you win together, you lose together but as forwards, scoring two goals in the last four games, creating 52 attempts on goal, it’s easy taking all the praise I have been there myself, but sometimes when you miss opportunities, glorious chances to score, you have to take responsibility as forwards who are in there to score goals.
“As well and as much as we praise them, Kyogo and Giakoumakis they must be looking at each other thinking we should have done better in the Champions League.”
The next Champions League game, against Shakhtar Donetsk, is a make-or-break one for Celtic and the duo will be hoping to give a better account of themselves in terms of goals in that match later in the month.
