"We've all had similar kinds of injuries, so we're all helping each other," Campbell told BBC Newcastle.
"It's good, keeping each others heads up and helping each other through it."
Campbell added: "I've been through stages that Michael might have been through and Michael's been through stages that Lee might have done.
"It's been a massive miss, watching every game that I can, and it's been a different six months but I've got to take the positives from it.
"I've seen another side of football which is hard work, and gruelling but you've got to do it if you want to see the benefits on the other side."
The former Manchester United forward suffered a ruptured knee ligament in August's 1-0 win against Manchester City.
Meanwhile another of Sunderland's long-term absentees is Republic of Ireland midfielder David Meyler.
The 21-year-old returned from a cruciate ligament injury picked up in the penultimate game of last season in December's goalless draw with Fulham after eight months out, but suffered another separate knee injury in January's 1-0 win at Aston Villa.
"All the lads are really gutted for David Meyler, he's a top guy, who had some really bad luck," Campbell said.
"He's sound in his head, mentally strong, so I'm sure he'll come back stronger.
"It puts it in perspective, when he's been out for a long time and he's still coming in happy, smiling to training.
"It makes you think I've got to be happy how I am and hopefully I can be back soon."