The on-loan Sunderland striker suffered a kick to the buttock during Tuesday night’s Papa John’s Trophy clash with Port Vale.
And it has caused a ‘massive swelling’ – much to the amusement of his teammates.
Rotherham boss Paul Warne said: “There’s a massive swelling on his lower back and he looks a bit like Kim Kardashian.
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“The lads have all stopped to have a look at him with his ‘keks’ round his ankles and have been laughing at him.
“I was saying after 20 minutes on Tuesday, ‘Is that how Griggy normally runs?’ He was running like a mermaid.
“He’s not as sore as we thought he would be. It’s like a dead leg. Whether he will be able to move enough to be involved on Friday I honestly don’t know.
“On Tuesday night I was sure he’d be out but now there’s a bit of hope.”