Jordan Nobbs' serious knee injury is a "big blow" to England's World Cup chances in France next year, according to record goalscorer Kelly Smith.
The player Smith describes as the "engine" of England's midfield ruptured her anterior cruciate ligament during Arsenal's win over Everton on Sunday.
Nobbs, 25, has 56 senior international caps and was England's player of 2016.
"She's a pivotal part of the England set up and it's a massive loss to both Arsenal and England," Smith said.
"It's going to be tough for her to make the squad, it seems."
Nobbs scored in the 4-0 win over Everton, helping the Gunners maintain their perfect start to the Women's Super League, where they sit top of the table.
But both Arsenal and England could lose the energetic midfielder for between six to nine months, which is the expected recovery time for ACL injuries.
Phil Neville's England team will go into the World Cup, starting on 7 June, as one of the favourites, having finished third in 2015 in Canada.
Nobbs did not play in that tournament because of a hamstring injury, but was part of the squad.
"As vice-captain and captain, Jordan and Steph Houghton are the first two names on the team sheet," former Arsenal and England forward Smith told BBC Sport.
"No one player makes a team, but when you're playing so positively and full of confidence, it's a blow to the team. She is the engine so it's a big blow."
Smith, who also suffered the same injury during her playing career, said making the squad in such a short space of time would be a "massive feat".
"It depends on the surgery and how she reacts post-surgery," Smith added. "Any time you come back from a long injury like that, it's a massive feat to come back in such a short period of time between now and the World Cup.
"Anything is possible but you don't know and you have to keep a positive frame of mind because you might have a couple of setbacks.
"It will be tough for her but I'm sure she knows that. I pray she comes back because she's an integral part of the side."