Paul Cook admitted Pompey need to show their ruthless streak in the final third.
And the Blues boss called on Michael Smith to find his killer instinct to get his campaign firing.
But Cook underlined his conviction Smith can be the man to fire his side to League One this season.
Pompey drew an attacking blank in Saturday’s 0-0 draw at Crewe.
Cook’s side failed to make their mark, despite there being a steady stream of deliveries into Crewe’s penalty area.
The Blues manager feels there needs to be more aggression from his side in penalty area.
Cook said: ‘We’re just lacking a little bit in that area at the minute. It’s a valid point for anyone to make.
‘But that will come with games and people playing together.
‘I felt we had enough quality to score, but we’re not aggressive enough in those areas at the moment.
‘That’s Michael (Smith), Curtis (Main) and the other lads but we’re getting used to each other.
‘We need 10 to 15 games for things to shape up. That’s football.
‘It’s us at the minute. We just lack that little bit of cutting edge in the final third.
‘That will come with people playing together and building relationships.
‘We just lack that little bit of assertiveness and a ruthless streak.
‘Michael’s got to find that within him. He’s come from a team like Swindon where everything is played and passed well.
‘We put some good balls in the box and we’ve got to find that ruthless streak in there.
‘It’s important to find that person, and I believe Michael will develop into that player. He’s got to do that.
‘The biggest thing in football is confidence. When you have it it’s great and when you don’t, all of a sudden it can affect you quickly.
‘My job is to take all of that away from him.’
With Main, Conor Chaplin and Noel Hunt waiting in the wings, whether Smith should be starting up front is a talking point among fans at present.
But Cook felt his attacking trio behind Smith weren’t firing.
He said: ‘Our flair players weren’t at their best.
‘Roberts hasn’t had as good a game as he’s had for a bit and Baker was disappointing. But they are good players, come on.
‘If we keep them fit they will show the talent they have.’
Despite there being black marks in Pompey’s performance, Cook saw reasons to be cheerful, too.
A clean sheet and the form of Kal Naismith, as he slotted in at left-back with Enda Stevens injured, were among them.
Cook said: ‘I don’t think Kal did a lot wrong.
‘He got forward and put in some smashing deliveries. He’s got a lovely left foot.
‘But Enda won’t be out for long.
‘It’s pleasing to have conceded one goal from the two games, too.
‘It’s quite funny it was an open game but had no goals.
‘We started well but we have that little dip in the game where we make mistakes in possession.
‘But you take positive points away from it.
‘We are probably two points behind where we want to be but there’s time to make it up.’