Brendan Rodgers has called for Celtic to sharpen up in the final third as they prepare for Europa League action.

The Hoops host Rosenborg in Glasgow in their group stage opener on Thursday.

Celtic scored 126 goals across all competitions as they completed the Double Treble last season but so far they have been unable to replicate that cutting edge this time out.

The Scottish champions were shutout by St Mirren on Friday, the second time they have failed to hit the back of the net this campaign, and have passed up opportunities to nail home the advantage with further goals in recent 1-0 wins over Hamilton and Rangers.

Rodgers, who revealed defender Kristoffer Ajer is a big doubt for the Group B clash with a virus while fellow defender Jozo Simunovic remains sidelined with a knee injury, called for his side to rediscover it's cutting edge.

He said: "We have to try and improve our level of performance, my trust in the players is 100 per cent, however we need to improve, especially in the final third of the pitch.

"Defensively, we've been solid but we need to do more in the final third.

"It's about ensuring that energy, that quality and about being clinical. That's what we have focused on in training and will look to bring into these next games."

Asked if the Hoops' recent prolificacy in front of goal was surprising given the potential goalscorers at his disposal, he added: "Potential, like you say. You don't win the game on paper, you win it on the field.

"We have lots of players who can score but we have to be more demanding of ourselves, that's our message.

"We can penetrate more, possession is no good on it's own."

Rosenborg are preparing for a second trip to Glasgow, this time for Europa League action after the Norwegians suffered defeat in Champions League qualifying earlier in the season.

While Celtic eventually failed in their own bid to reach the lucrative group stage of Europe's premier competition, Rodgers reiterated his excitement for European football remains strong ahead of the Europa League opener.

He continued: "There is always excitement going into the European competitions and this is no different.

"It is a real good group we are in.

"It's where we deserve to be, we're not entitled to be in the Champions League, we didn't qualify, as simple as that.

"We're in the competition we deserve to be in, we respect that and it's our duty to go and get as far as we possibly can."