Scott Higginbotham says James Slipper's private persona meant he never knew the full extent of his troubles.
The Queensland and Wallabies veteran copped a two-month ban and $27,500 fine from Rugby Australia after it was revealed on Thursday he had twice tested positive to cocaine this year.
Reds captain Higginbotham, a good mate of Slipper's, said he knew of the prop's mental health struggles but didn't have "any idea" about his drug habit.
"I'm sad for him; being a mate, what he's been going through outside of football is not something you want to see," Higginbotham said.
"You think you're a close enough mate that he'd explain to you and tell you everything.
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"But that's the circumstances; he's a cagey sort of person, likes to keep things to himself, keep them on the inside and we didn't have any idea."
Slipper's suspension follows a series of drug indiscretions from Reds star Karmichael Hunt, who is yet to play for the club this Super Rugby season despite being cleared for a return since March.
But Higginbotham dismissed the notion that there was an issue with drugs at the club.
"It's not concerning ... every person's different aren't they," he said.
Slipper, 28, is off contract beyond this season and faces the prospect of never playing for the club again if coach Brad Thorn opts to take the same hard line stance he has adopted with Hunt.
But club chairman Jeff Miller insisted on Thursday that Slipper's supreme track record and current circumstances meant he was a special case.
Higginbotham would love to see him back at Ballymore but won't be pushing him to return.
"You want the best thing for him; first and foremost he has to get himself righ mentally, sort out these off-field issues," he said.
"Once he's done that and ready, that's when he'll play."
