Liverpool defender Glen Johnson sustained a hamstring injury despite coming on as an 81st minute substitute on the weekend and now the club is unsure of how long he will be sidelined for.

Johnson returned to the Reds line-up for Saturday's clash with Stoke City following a thigh injury but was injured after replacing Martin Skrtel late in the 1-0 loss.

Reds first team coach Steve Clarke says he will not speculate on the length of absence for England full-back Johnson who has a tough time of it recently.

"We are still waiting on the results of Glen's scan so until that comes out there's no point in speculating about it," he told the club's official website.

"We will just see how he is when we get the scan and see what the timeframe is."

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