Campbell, who turned 28 last month, played 116 games across eight seasons for the Hawks.
Despite the onset of the knee injury in 2005, Campbell played 70 of a possible 71 games from 2006 to 2008.
However, he managed just 14 in his last season, which led to his retirement announcement at last year's Peter Crimmins Medal count.
With Max Bailey and Simon Taylor both recovering from long-term injuries this season, the Hawks have sorely missed the competitiveness and versatility of the 199cm big man, who has also played as a key back.
Hawthorn coach Alastair Clarkson gave cautious support to Campbell's audacious comeback bid, but said a return to AFL football was still a long shot at this point.
"He's got a lot of hurdles to cross. The most significant one of all is the health of his knee," Clarkson said from Waverley Park on Friday.
"We made a decision with Robbie and the medicos at the end of last year that the health of his knee long-term was the most important thing. He's elected to give it a go because he's just been feeling so good with being able to rest his body.
"We'll see how that goes, and if he gets into a position where he can recover really well from games and makes good contributions, then maybe he's a chance sometime to return to AFL footy, but that's so far-fetched right at the moment.
"He just needs to get himself up and match conditioned. His first real goal is to make a contribution at Box Hill, and we'll see where that goes from there."
Campbell, who played uner-18 footy with the Murray Bushrangers, joined Hawthorn as a rookie, and made his debut against Richmond in round five of the 2002 season.
