He explained: "Benfica play football, that's their style. So, when they smother a game, they do it in a different way from others who come to Celtic Park and try to kill it by man-marking, keeping it very tight, playing three at the back, and flooding the midfield.

"Benfica do it by keeping the ball, and we have spoken to our players about what this means, because we discovered over in Lisbon how tired you become when you are the ones doing the chasing. Benfica are a good side, but it is vital we win. We can't play as though it is vital - that would leave us open. We can play with enthusiasm, but must always focus on how we move the ball and keep it."

Strachan admits tonight will hinge on Scott McDonald and Jan Vennegor of Hesselink getting the better of Benfica's defence.

He said: "That's why we had to get Jan a bit of a game in midweek against Hearts and another 90 against Kilmarnock on Saturday. Everyone knows our big two at the moment.

"Now, that can change. But you don't change because someone comes in and does well in a game or two.

"Say Scott got injured next week and I put someone else in who scores a couple of goals. When Scott is fit again, do I leave him out? Or do I say to him that for all that hard work you have done for us, there is no way it can be destroyed by someone else's 90 minutes on the pitch?

"To earn that place, you have to show over a period of time you are ready to replace someone. You just can't say after one game, right that's it.

"When Jan, who is our main striker, is fit, we have to try and get him back into our side."