The weather offered a metaphor for what was to come; unsettling questions regarding the form of an expected talisman in Bjorn's European Ryder Cup team.

But amid concern for Sergio Garcia's game there was a discernible calm from the captain for next month's match. Bjorn is a skilful operator when it comes to defusing difficult issues, but he knows this week's tournament is pivotal to the qualification process for both sides.

• Spieth relaxed over second attempt at career Grand Slam

Garcia is struggling, six missed cuts in his last 10 events, and the Spaniard needs to turn things around. The 2017 Masters champion is 20th in European points and 12th on the world ranking points standings.

Only the top four on each list gain automatic qualification.

But for a major champion who has played eight Ryder Cups, the key now is to show a degree of form rather than qualify outright.

"He is a world class player, the type of player who can turn it around in a week or two," Bjorn stated.

But the Dane is also aware that Garcia is not performing to his expected level. He missed the cut at the Open at Carnoustie, didn't make the weekend at the Canadian Open and finished tied 39th in the no cut WGC Invitational at Firestone last week.

"Sergio won't be happy with where he's been with his game over the last few months," Bjorn admitted.

"I'm sure Sergio would like to go out and put in a few good performances because that will make him feel good about where he is.

"Knowing him very well, he tees it up every week to try and go and win golf tournaments and I would like to see something from him."

Bubba Watson and Jordan Spieth are hoping to secure their Ryder Cup places for the USA ahead of the likes of Bryson de Chambeau, Phil Mickelson, Xander Schauffele and Matt Kuchar

The plus side for Bjorn is that the one event Garcia has played well at in recent weeks was a top 10 at the French Open at Le Golf National, which will stage the Ryder Cup.

"If he doesn't make it on merit, does he fit in there with where he is going through all of those points that I put down of making my picks?" Bjorn said.

"For Sergio's sake, I would like to see him probably putting in a bit better performances than he has because he's such a quality player and he brings so much to the European team when he's on form."

• US PGA tee times

Of course, the US PGA Championship is a standalone major in its own right and carries its own resonance. But there is no doubt that this week for the 100th running of this tournament it is to be largely seen within the Ryder Cup prism.

The likes of Garcia, Henrik Stenson, Ian Poulter, Russell Knox and Matt Fitzpatrick can take significant strides towards automatic qualification for the European team.

It is also the last event where players can cement their spot in the American side.

Already four players are guaranteed their place in Jim Furyk's line up; world number one Dustin Johnson, Brooks Koepka, US PGA defending champion Justin Thomas and Masters winner Patrick Reed.

The next best placed players are Bubba Watson, Jordan Spieth, Rickie Fowler and Webb Simpson, and their automatic spots could come under pressure from Bryson de Chambeau, Phil Mickelson, Xander Schauffele and Matt Kuchar.

Then there is the question of Tiger Woods, who lies 20th in the standings but on current form and career reputation looks increasingly unlikely to be ignored for a wildcard pick.

There is no doubt both captains will be watching very closely the progress of their likely team members as they take on the Bellerive Country Club.

It is the last time the US PGA will play such a pivotal role in Ryder Cup selection because from next year it will move to its new May date, leaving the Open as the final major of the year.

The St Louis course was battered by those early Tuesday thunderstorms, leaving ideal conditions for someone like McIlroy to prosper. He is a two-time US PGA winner and loves the way they set up tournaments, especially when conditions are soft and receptive.

Another European win, following Francesco Molinari's Open triumph, would provide a strong ray of sunshine for Bjorn - with the clouds further clearing if Garcia can put himself in the mix.