Defender Richards was carried off on a stretcher after pulling up less than three minutes into the England Under-21s' 4-0 thrashing of Denmark in Viborg.
The injury-plagued 22-year-old claimed afterwards he would be out for four weeks, which would rule him out of the April 16 Manchester derby at Wembley, but head coach Stuart Pearce insisted no medical prognosis had been given.
Early finish: Micah Richards lasted just four minutes against the Danes
'He's got a hamstring problem and he's diagnosed himself as being out for four weeks - that's Dr Richards for you,' Pearce said.
'That could be four days though, as that's him diagnosing himself! Let's hope for Manchester City's sake and the preparation in the summer that it's not too long.'
Pearce insisted England still had plenty of room for improvement ahead of June's UEFA Under-21 Championship finals, despite yesterday's crushing win over the tournament hosts.
Pearce's youngsters rediscovered their ruthless streak, having failed to win - or score in - their previous three matches.
Happy with his lot: England under-23 manager Stuart Pearce
However, although they clinically took advantage of defensive errors made by the Danes, they produced a string of their own which went unpunished in Viborg, where they will return in June for their final Group B match against the Czech Republic.
Pearce said: 'I was pleased with the result and the clean sheet, but I was disappointed with the first-half performance as we didn't play particularly well and we were too open in midfield and allowed the opposition too many chances.
'In the second half, I thought we improved. In international football, to win a game is hard work, make no mistake. To win 4-0 away from home, I am very pleased with.
'For me, it's a stepping stone towards the summer and hopefully one or two players showed me they're improving and getting better. It's me collating the squad basically.'
England do not have long to learn from the mistakes made tonight, with Pearce's side facing Iceland in Preston on Monday night in their penultimate friendly before they return to Denmark for June's first finals match against Spain.
'I've only got two games left now before we step out against Spain,' Pearce added.
'We have to keep improving, we have to be full at it every game. I don't think we were today, but it was good enough to win the game.'
England's strikers looked particularly sharp, with Danny Welbeck, Scott Sinclair and Daniel Sturridge all finding the net before Jordan Henderson slotted in the visitors' fourth goal.
Bolton's on-loan Chelsea forward Sturridge stole the show, as Pearce acknowledged.He said: 'There was some decent performances in there, Danny Welbeck coming back from injury and Sturridge was outstanding, as was the goalkeeper (Alex McCarthy) in his first start.'
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