Cousins suffered a grade-one hamstring tear six minutes into the last quarter on Thursday night at the MCG.
It capped a shocking night for the Tigers, who lost by 83 points.
At three-quarter time, medical personnel were looking at the back of Cousins' left knee. But he said that was an unrelated issue to his hamstring.
There has been widespread speculation about why he returned to the game, given his history of hamstring injuries and the fact that Richmond was well behind.
Cousins insisted that any criticism of the support staff was unjustified.
"I was confident to go back on, I wanted to go back on, because I thought I was in a position to do that," he told Channel Seven.
"I couldn't speak more highly of the way they (the medical staff) have got me from the point I was, then to the point I was in round one.
"I couldn't have done anything more to be prepared.
"I am 30, I've had 18 months out of the game, I was going to cop some sort of injury at some point, you would think."
Cousins said he had experienced tightness behind the knee before in his career and said it was only a "niggling" problem.
"With the work I'd done with the medicos, I was 100 per cent confident - and still am - that's what it was," he said.
Cousins is encouraged by the diagnosis and the Tigers say he should be back in three to four weeks.
"It doesn't have to keep me out of the game for six weeks," he said.
But fellow Brownlow Medallist Nathan Buckley, who interviewed Cousins, is not so sure.
Buckley had well-documented hamstring trouble towards the end of his career and he thinks Cousins might have to sit out more than a month.
He added Cousins would probably have to resume in the VFL with the Tigers' affiliate Coburg.
"I'd suspect they might be even more cautious than that (four weeks)," Buckley said.
"The only issue is what's best for Ben Cousins and his football ... I reckon he would have to (play in the VFL)."
Buckley said Cousins seemed very realistic and optimistic about this latest setback to his career.
"He is a very focussed individual, he's a very professional footballer, he does everything - dots the Is and crosses the Ts," Buckley said.
Cousins described the injury as a minor hiccup, but admitted he felt shattered and angry, particularly because it was another hamstring injury.
"Footy is the easy bit - this hamstring, although it's going to be hard to deal with in some respects, it's the easy bit (compared) to where I've come from," he said of his drug addiction.
"God works in mysterious ways and things have a funny way of working out.
"This could be a blessing in disguise, for me and for Richmond - we've got that out of the way now.
"We have a lot of work to do, it was a huge reality check, in my mind we're a lot better side than that."
