Ronny Deila wants his Celtic side to maintain a lead with a lot more conviction.
The Hoops boss was speaking after the 1-1 Europa League draw against Astra Giurgiu in Romania last night.
The Group D fixture was in doubt due to fog, but midfielder Stefan Johansen cleared the way for qualification to the last-32 of the competition with two games remaining when he gave the visitors the lead with a powerful strike in the 32nd minute but that was cancelled out in the 79th minute by Astra substitute William Amorim.
Substitute Leigh Griffiths, on for Stefan Scepovic, had the ball in the net with minutes remaining only to see it ruled off for an infringement before Astra's Vincent Laban was shown a straight red card for a foul on Charlie Mulgrew in injury-time.
Deila, however, believes the game should have been secure before then.
The Norwegian said: "Maybe we could have attacked more but we seemed quite confident and had control.
"I am frustrated by that and we have something to work on when we go 1-0 ahead.
"We have to keep on playing offensively instead of trying to win the game 1-0. We should go for more.
"The performance was OK, the results should be better."
In the group's other fixture, Salzburg beat Dinamo Zagreb 5-1 to go through the knockout stages with 10 points and two games to play.
The Austrian side travel to Celtic Park later in the month before the Hoops visit the Croatian club away in December in their last fixture.
Deila said: "It was two points lost.
"We were the best team in the first half we were excellent and scored a nice goal.
"In the second-half we controlled it quite well but they scored a fantastic goal.
"There was nothing we could do about it - it was a fantastic shot.
"But they didn't have many chances against us.
'We had enough chances to kill the game and to win it, but in the end we have one point and while I am not happy with that, it is better than nothing."