SYDNEY, Australia -- Of all the players England could not afford to lose for this Women's World Cup, midfielder Keira Walsh is top of the list. The 26-year-old is the beating heart of this team, a world-class operator, and indispensable to their transitional game. She's irreplaceable. So the sight of her covering her face as she was stretchered off with what looked to be a nasty knee injury against Denmark took any gloss off another 1-0 win that has England on the verge of the knockout stages of the World Cup.

It's no coincidence that Walsh's injury in the 35th minute kerbed England's dominance. From a mental point of view, it must be brutal for her teammates to see one of their own in that much pain. From a functional, tactical perspective it completely threw the team.

- Women's World Cup: Landing page | Schedule | Rosters | News

To understand Walsh's importance to England, take note of Ellen White's words. Now retired, White started each of England's matches in the Euros last summer.

"At the Euros everything came through Keira," White said on the BBC. "There wasn't a Plan B. I dreaded to think of the idea of us ever losing her because she was one of our best players. Beth Mead was scoring all the goals but all of our play came through Keira. She was the key cog, everything moved through her. I just don't know who England are going to have now in that No. 6, or even potential double No. 6, role."

On Wednesday, 48 hours before England faced Denmark, Walsh sat in front of a group of media and talked about what it's like to be one of the most targeted players in world football. Teams know that if they can stop Walsh from playing her natural game -- just like Haiti did -- they can cut England down at source.

Walsh said she had a few plans up her sleeve and for the first 35 minutes against Denmark, she was magnificent. She relished the attention as her opponents tried to press and pull her out of position, but with a sleight of touch and an odd drop of the shoulder, she was able to pull the strings and orchestrate England's attack.

It was -- for half an hour -- far more precise than the 1-0 win over Haiti. All week England talked about ruthlessness, and we saw that 75 minutes before the start of the match. England manager Sarina Wiegman made two changes: Lauren James starting on the wing, Rachel Daly at left-back.

England went the entire Euros without making a single change to their starting XI -- blessed with the lack of injuries, it also spoke to Wiegman's philosophy where more often than not, she picks a group and sticks with them. But the Haiti win, and the unconvincing performance, led to the manager making changes. And it clicked.

James needed just six minutes to show why she's one of the most admired young forwards in world football and justified Wiegman's decision. Daly provided the assist as she found the Chelsea forward on the edge of Denmark's box; James dropped her shoulder, glided past a defender, and hit a beautiful curled shot into the bottom left corner of Denmark's net. It was a sublime moment.

With centre-back Alex Greenwood's distribution allowing the team to bypass Denmark's high press, England continued to dominate territory and possession, but then came the Walsh injury. As she stretched for a wayward pass, her right leg seemingly caught in the turf and her knee buckled underneath. She immediately signalled to the referee. Two teammates came to help, but Walsh waved them away as the physios ran on. "I've done my knee" she seemed to tell them. And after a handful of minutes, she was stretchered off.

Forced into another change, Wiegman turned to Laura Coombs, putting Georgia Stanway into the No. 6 role, Coombs into No. 8, and Ella Toone still as a No. 10, but dropping deeper when needed.

England didn't have the same fluidity, their effective transitions weren't quite as slick, and the half-time whistle was needed to allow them to regroup. Walsh's absence was stark; England's errors mounted up and Denmark switched to a more attacking 4-3-3. Passes were misplaced and Denmark found joy through the middle in bisecting the two centre-backs and getting into dangerous areas.

England had goalkeeper Mary Earps to thank for a world-class save late on against Haiti to preserve the win, and this time were grateful for Earps' left post as Amalie Vangsgaard's close-range header in the 89th minute struck it instead of finding the back of the net. They eventually held out and with qualification all-but secured -- another 1-0 win, another clean sheet -- a collective exhale could be breathed.

But this team are already without the spine that won the Euros. White and Jill Scott are retired, with Leah Williamson, Beth Mead and Fran Kirby all out through injury. Optimists will look to that offering opportunity; pragmatists will point to that weight of absent talent and the gaps they leave. If Walsh's injury is as bad as feared, then this is yet another brutal blow and a test of their depth.

For 35 minutes it looked like the story of this match would be the one where James announced herself on the international stage. Instead it was the match where Walsh picked up the injury. After that, the team showed monumental heart; they rallied, regrouped and found a way through. It was scrappy, but again, England came away with three points. That speaks to the character of the group ... something Wiegman is incredibly proud of.

The next 24 hours will be nervous for England. They'll be keeping everything crossed that they'll have Walsh available again in this tournament. But if it is as bad as feared, Wiegman will need to find a Plan B to cope without their most influential player.