Iran , USA and Wales - England playing those 3 nations in the Group stages is similar to playing lessor opponents during an International break . There should be nothing to fear there - Wales will fight hard , but England should win that .
Remember Franco Baresi - USA 1994 - Got injured in the opening group match , flew back home , got treatment ( maybe even an operation of sorts ) , flew back afterwards and appeared in the final .
If a player has an injury from a country that would expect to go far , they might still get a game later on in the knock out stages , unless it's a long term injury .
I don't fancy England to beat any.of them in fairness.