England's Keira Walsh may play in last-16 game, says Sarina Wiegman

"She's doing well," Wiegman told reporters on Sunday. "She has been on the pitch, training today and now we will wait to see how she recovers and if she does well then she will be available for (Monday)."

Sunday was Walsh's first training session with the team since suffering a knee injury on July 28th. She left the pitch on a stretcher with what looked like a serious knee injury during England's 1-0 win over Denmark.

"It was a very hard moment and not nice to see," said Wiegman, who would not give details on the injury except to say it was not a ligament.

"Everyone was in shock of course. But then really quickly, the day after, we knew things weren't as bad as it looked and people thought."

England won all three group games to finish top of Group D.

Walsh is considered one of the world's top midfielders, signing a three-year contract with Barcelona last September for a world-record fee of around 350,000 pounds ($400,000).

Although Nigeria are 36 spots below fourth-ranked England, Wiegman said the tournament has shown that every team is a threat and praised the depth of the 32-nation field.

She looked aghast when a reporter asked if England had to "guard against complacency".

"Absolutely not. What we have seen in this tournament is that nothing is easy," she snapped. "The growth of the game has shown in this tournament. We've not had an easy game at all and that's what we expect (from Nigeria) – that it will be very competitive and we need to be at our best."

England are considered among the tournament favourites as European champions. They are unbeaten in 35 of their last 36 games.

"Everyone who plays us wants to beat us," Wiegman said. "That's nothing new. What we have seen in this tournament is game is developing really quickly. The games have been very competitive. Nobody can be complacent because that's inappropriate. It's very tight."

Wiegman, the last female head coach remaining in the tournament of the original dozen, was praised for changing up her formation in the rout of China, reducing her back line from four defenders to three.

"We have two options now – the way we have played and what we did against China so we will take into consideration," Wiegman said.

The Lionesses are making their sixth World Cup appearance. Their best finish was third at the 2015 tournament in Canada.