Arsenal striker Danny Welbeck is facing six months out injured, according to England manager Roy Hodgson.
Arsenal announced last week that Welbeck has undergone surgery on his left knee and will be out for "a period of months."
The former Manchester United forward has 33 England caps to his name but has not represented his country since March.
Hodgson is concerned about his long-term absence as well as a lengthy period on the sidelines for Liverpool's Daniel Sturridge.
He said: "Well, Welbeck bothers me now. He has already been out for me since March and for Arsenal since April, so that's over four months, isn't it? And now I hear it's another six months, so I can only hope that Danny recovers a bit quicker and then hits the ground running.
"Daniel [Sturridge] is a bit the same. It's getting on for a year now [since he played for England]."
Hodgson, whose side beat San Marino 6-0 on Saturday, added: "They are always in my thoughts because I think they're very good players and they did extremely well when they were playing in the national team I was coaching, but I've got to make certain that there are a few [Jamie] Vardys and [Harry] Kanes and [Theo] Walcotts, because we can't keep going around talking about the ones who aren't there.
"What we're trying to develop is a bigger pool of players, to get that pool up to 30‑odd where we can say: 'Whatever happens, as long as we can get 23 of this 30, we'll be OK.'
"Then you would have to be unlucky if two or three in the same position go down.
"We don't need more than 30. It wouldn't help to have 900 players playing in England because you can only work with 23 to 30. So that argument, I think, needs to be properly debated because it's not that important how many English players are playing in their teams. It's more important to have pathways for those we might have in the future."