The 30-year old centre-back has been brought in for the rest of the season to help with the Hammers' injury crisis after spending the first half of the campaign with Sheffield Wednesday.
In addition, Jack Sullivan, the son of co-chairman David Sullivan, posted the following on Twitter.
ROGER JOHNSON has signed till the end of the season, as emergency cover at CB. He might surprise a few people. More news soon— Jack Sullivan (@jsullivanwhu) January 6, 2014
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