Celtic's Norwegian defender Kris Ajer warned his Hoops teammates they must be fully focused if they are to advance in the Champions League against Rosenborg.

The Scottish champions cruised through to the second round of qualifying by comfortably dispatching Alaskhert over two legs 6-0 on aggregate.

Celtic's reward is a repeat of last season's qualifier against Rosenborg, who secured their own passage through thanks to a controversial last-gasp penalty against Valur.

Brendan Rodgers' men edged out the Trondheim outfit 1-0 on aggregate last season and Ajer expects another stern test to lie in wait for the Hoops when Rosenborg visit Parkhead next week.

He said: "Rosenborg are a really tough opponent with a lot of quality players.

"It will be a really tough game, both home and away.

"When you play Champions League qualifiers, you meet quality opponents."

He added: "I know Rosenborg really well. Last year, they beat Ajax in the last round to go through [to the Europa League group stage], so they are a really top side and can really hurt you if you're not 100 per cent up for the game.

"But we know that, when they come here next week hopefully we can put in a top performance."

Former Arsenal forward Nicklas Bendtner struck twice as Rosenborg overturned a 1-0 loss in Iceland to scrape through to round two.

Ajer insisted his home nation's big hitters are built upon astute organisation, rather than relying on a star performer.

"Rosenborg are a typical Scandinavian team," he added. "They are well organised and have a good squad, so I think that's their biggest strength.

"We need to be 100 per cent focused, they are a great team so we need to be ready for that."