Van Gaal told a news conference on Monday he did not know if injured defenders Martin Demichelis, Daniel Van Buyten and Diego Contento would have recovered in time to defend Bayern's 1-0 advantage from the first leg.
Ukrainian Anatoliy Tymoshchuk has not even travelled to France.
"I've come here with 17 players and I can only field 11 so if I miss the three others, I'll still have 14 available players," the imperturbable Van Gaal said.
Bayern have the worst defensive record of the four teams still in the Champions League, having conceded 13 goals this season in Europe, but Van Gaal said the most important thing would be to score.
"We are not the kind of team whose aim is just to avoid conceding goals when we enter the field. I've never told my players to play like that since the beginning of the season and I won't start tomorrow," he said.
Fellow Dutchman Mark van Bommel, who missed the first leg through suspension, said he was not worried about his side leaking goals.
LACK OF EXPERIENCE
"We have often conceded goals in away games this season but that's not a problem because even if we concede six goals tomorrow and we score five, we're through," the Bayern captain said.
Van Gaal said he was confident his team would overcome their injury woes thanks to their German mentality, which helped them knock Fiorentina and Manchester United out on away goals in previous rounds.
"Our willpower is just incredible, we have always managed to stay alive this season even during games when we were trailing," he said.
"When I was a coach in the Netherlands and my team had to play against a German one, I used to tell my players that they had to be ready to play until the very end of the game.
"Our team is made up of German players and foreign players who have been playing in Germany for quite a long time and are now immersed in this special German mentality," he said.
But Lyon coach Claude Puel warned Bayern they did not see the real Lyon in the first leg.
"Bayern feel confident, that's fair enough... but we know we are able to overcome any European opponent if we play at our real level," Puel told reporters before going to the Gerland pitch for training.
"We've had to go through difficult moments this season in the Champions League and we've always been able to raise our level each time we had to," he added.
Puel said Lyon, who knocked Real Madrid out in the last 16, suffered from a lack of experience in Munich.
"Let's not think about the situation and just focus on what we have to do on the pitch... Let's focus on our own game, which, I repeat, is not what we showed during the first leg," he said.
Lyon captain and defender Cris, whose knee locked in the first leg, said he was confident of making the starting line-up.
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