Warren Gatland has revealed fly-half Gareth Anscombe will have a hospital scan on Monday amid a scare over his fitness for the World Cup.
Wales' first-choice No.10 hobbled off in the first-half of the 33-19 Twickenham defeat to England and was replaced by Dan Biggar.
Anscombe was then seen on the bench with crutches, prompting Sky Sports pundit Chris Robshaw to say it looked a worrying problem for him and Wales.
Anscombe had tried to play through the pain barrier by staying on the pitch, but looked in clear discomfort and eventually had to be helped off by two Wales medics.
Asked about the extent of the injury, Gatland said in his post-match TV interview: "We're not sure yet. He will get a scan tomorrow and we'll see how things are then.
"I’ve spoken to the physios. He’s got to get a scan. If it’s a strain, he’ll be out for a few weeks. We’ll find out. I wouldn’t want to be naming my team on Monday."
Asked about Anscombe playing on, instead of coming off straight away with the World Cup around the corner, Gatland said: "The message was to see how it goes. He didn't do any further damage to the knee by playing on, it was already done.
"Players see if they can run off a knock, he wasn't able to do that."
Of the Welsh performance, Gatland said: "We just didn't play very well. There were a couple of soft tries conceded, but that happens when teams are trying to put some combinations together.
"England went back to what they are traditionally good at, scrum and lineout were good. We tried to play a bit differently today, we'll see how to approach next week.
"Any loss is not good, but this is not competition phase. The Six Nations is competition, the World Cup is competition. We'll look at the positives, some of the opportunities we created and we will be a lot better next week."
Wales were never able to recover properly after conceding two early tries, but skipper Alun Wyn Jones refused to blame rustiness.
"We could probably use that as an excuse, but we're too professional to do that," he said.
"We know where we are. We have another opportunity against England next week. This is the first one on the journey this season, we're well on the way."
The Twickenham clash was the first of four World Cup warm-up matches for Wales. They meet England again in Cardiff next weekend, followed by back-to-back games with Ireland.
The tournament then begins in Japan with a Pool D clash against Georgia on Monday September 23.
