Sergio Conceicao has admitted Porto will be loath to take any risks with Sergio Oliveira's fitness in Tuesday's Champions League clash with Chelsea.

Porto trail Chelsea 2-0 at the midway point of the quarter-final, with the Blues acting as the home side in the second leg in Seville.

Oliveira has scored 17 goals in all competitions for Porto and can return after suspension, but boss Conceicao is not sure whether he can manage 90 minutes.

"We will see tomorrow," said Conceicao.

"As you know, the last match as I can say, he was not yet ready for the 90 minutes because of a small muscle problem and it is always dangerous.

"This is an important part of the season, we are fighting. We have some very demanding matches ahead of us so we have to ponder a lot between players who are players who are fit and those who aren't so we will see what is the best 11 to face Chelsea.

"Also, when you want to get players back too fast it can be harmful.

"We need to be cohesive and compact. We also need to score and not suffer, that has to be our match strategy."

Porto have to throw caution to the wind and will need to score at least three goals to turn the tables on Chelsea and reach the semi-finals.

Conceicao gave short shrift to the idea of altering his side's tactics, but insisted Porto can still take the fight to the Blues.

Asked if he would deploy more attacking players to chase the game, Conceicao replied: "I'll answer in a very simple way, and be very assertive: it's not with lots of forward players that we attack more or with more defenders that we defend better.

"We have to score. Be well balanced at different times of the match, but most of all we have to score. One goal at a time because we can't score two at the same time.

"But that calm and serious way of thinking, knowing what we have ahead of us is important without being too anxious.

"We just have to focus on the work and not the final result, because we have to work to reach the end result, to achieve our goal."