Celtic assistant manager Chris Davies has revealed that Brendan Rodgers has been "reinforcing" the importance of defensive concentration ahead of the Europa League tie against Zenit St Petersburg.

The Parkhead side go into the knockout tie on track to make a successful defence of their domestic treble but have shown some slips at the back in recent matches, notably when a Jozo Simunovic error allowed Partick Thistle back into the Scottish Cup match on Saturday.

While Davies said that individual errors were in the past, he said concentration had to be high when they go up against a side he believes are "one of the better sides" left in the Europa League and are the top scorers in the competition so far.

"It's important that we're defensively good at this level, we know that," Davies said. "It's something that the manager had been reinforcing, that concentration aspect of defending.

"Even more so when you're against top teams and top players. You have to be constantly thinking and constantly aware and that comes from the concentration side of it.

"That's something that the manager's been reinforcing and we have to be ready for."

Celtic host the Russians in the first leg and while the accepted wisdom is that the Scottish champions have to win at home to have a good chance of progressing, Davies pointed out that there were recent examples of that not being the case.

"I think you've seen in previous two-legged games that we've had that there's different [good] results," he said.

"Rosenborg, for example, we were 0-0 which maybe at the time didn't feel like the best result. But we kept a clean sheet and put ourselves in a strong position for the second leg.

"We went away and finished the job off so you have to really be in a position where you have a chance for the second leg. It's only going to be half time."

However, the coach was under no illusions about the scale of the task he thought his side would be facing.

"What's very important to acknowledge and respect is the level of the opponent we're about to play against," he said. "Having analysed and watched them now for a few months, individually and collectively they're a top team.

"They're a Champions League level team with quality. We have to recognise that, and respect that and be prepared for it."