After returning to the first team last year Johnson only featured twice, coming on in the 89th minute against West Ham in August and scoring in his side's 5-1 defeat of Scunthorpe in the Carling Cup in October, before suffering the knee injury five weeks later.
"No player wants to have to go through such a long recovery and it has just been bad luck that I have had two in a row early in my career," said Johnson.
"Having recovered from a serious injury before means that this time I am a little more experienced and can deal with the frustrations much better.
"I went down to see the surgeon for my 12-week check-up just a few weeks ago and he gave me the all clear. It looks as though the surgery has been very successful.
"The graft was strong and he told me to start building up my running now and start strengthening my knee again day by day."
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