Swans captain Williams picked up an ankle ligament injury in the 2-2 draw with Liverpool and has played just once in the intervening period, against Crystal Palace.
The Group A meeting with St Gallen will be the third game in a row that the Wales captain has missed, and he is very unlikely to feature against Southampton prior to the international break.
Coleman, who names his Wales squad on Thursday, will desperately want to include Williams in his team to play Macedonia and Belgium, with his position under scrutiny with the nation bottom of their World Cup qualifying group.
But Laudrup has urged the Dragons boss to put Williams' long-term fitness first, as he believes he is doing himself, although he has yet to speak to Coleman on the matter.
The Dane said: "We have not spoken, I haven't had time. Let's see what happens in the next few days and what we decide for Sunday.
"If Ashley is playing or not, I am saying he should still go with Wales so the medical staff can look at him and then do the best for one person, for Ashley - not Swansea or the national side.
"Because as a player if you know you are not 100 per cent, it's bad. If there are things you can't do because of injury it's not good and, at this level, if that's the case your levels will drop.
"I've spoken to Chris a couple of times previously. We all agree the most important thing is the player.
"It's the same for us. I could say if we win against St Gallen we move on to six points and are top of group. We also want to win at Southampton on Sunday, so they are two important games for us.
"But have to remember it is October 2 and we have to go on until May.
"I really want some of my injured players available for Thursday and Sunday, but we have to think long-term and what is best for them because that's the best for everyone.
"If they are not 100 per cent our general performance will drop and we cannot afford that. It can depend on the injury and so on but the players are the most important thing."
While the loss of Williams and the absence of Pablo Hernandez and Garry Monk, plus doubts over Angel Rangel's fitness are a blow for the Swans, there will be an expectation for them to back up their superb 3-0 win at Valencia in their first group fixture.
But St Gallen's play-off round success over Spartak Moscow, allied to Basle's Champions League win against Chelsea, serve as a reminder that Swiss sides are not to be taken lightly.
Laudrup said: "I've seen their game against Kuban Krasnodar and against Spartak Moscow in the play-off.
"They don't have the big stars but they really work hard.
"They were underdogs against Spartak, a side who have played in the Champions League.
"They drew in Switzerland and were 1-0 down after 51 seconds in the second leg and were then outplayed for 20 minutes.
"But suddenly they went 3-1 up, so it shows they have a lot character, it will be a difficult game and a game where even if we're doing well we have to keep an eye on the spirit in their squad.
"They play differently than us, a little more direct at times, but they have really done well against the Russians so I want to repeat we have to be careful.
"We are at home, we have to try and control the game, but be aware of counter-attacks and their spirit."
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