Hammers boss Glenn Roeder did not appear at the post-match press conference until over an hour after the final whistle, having been anxiously awaiting news of Carrick's fitness.
Carrick limped off in the 90th minute and Roeder revealed: "He's suffered an new injury to the groin that was operated on in February.
"We've known he's been feeling it a bit for the last couple of games and I took a bit of a liberty leaving him on for so long today."
Roeder said he would be phoning England Under-21s coach David Platt tonight to discuss the injury to the 20-year-old Carrick, who is a key member of Platt's side, along with Jermain Defoe, but the signs are ominous.
"It's really disappointing for Michael and I'm worried that if he has the injection he needs to ease the damage, it will be seven-to-10 days before he can play again. If he then gets the rest he needs, he'll be okay to start pre-season training on July 4."
But that will rule Carrick out of the Under-21 tournament and Platt will be bitterly disappointed. "I can't say whether he'll miss it until I've spoken to David Platt - and I'll be calling him tonight," added Roeder.