Mark Marshall is struggling to face his former club Bradford on Saturday.
The Charlton winger, who just returned from a knee problem, suffered a thigh injury in training last week.
He has been left out of the last two Charlton squads against Doncaster and Oxford United as a precaution.
But Robinson revealed Marshall’s injury is worse than first thought - and he could miss out on what would be his first return to Valley Parade since leaving in the summer.
The Charlton boss said: “It’s a little bit worse than we thought, his thigh. We thought it was a slight twinge, it is a very low grade 2, severe grade one, so it’s a little bit more intense.
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“It’s just a case of a little flick that caught him in an unorthodox position. Sometimes when you do that from a muscular perspective, you put yourself at greater risk of injury.
“He did something quite unusual and he felt a little twinge in his thigh and he stopped straight away so he got the immediate treatment. So it won’t be a massive injury.”
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