Reina's future was a subject for debate all last season, with the 30-year-old being linked with a return to former club Barcelona, and Mignolet's arrival only increased speculation about an impending exit.
But Rodgers is adamant Reina knew of his plans to strengthen the goalkeeping department and the Reds boss dismissed suggestions the £9million Belgium international was a straightforward replacement.
"I always felt it was important for us to have competition right the way through the squad, and that includes the goalkeepers," he said.
"I spoke to Pepe about this a few months back and told him we wanted to bring in another goalkeeper as real competition. I was very open with my goalkeepers and they know the situation.
"Pepe has been terrific here, Brad Jones was excellent when he stood in last year and I felt we needed another one. Simon comes in and we've got great competition and when you've got competition it pushes everyone to perform.
"We obviously lost a young goalkeeper in Peter Gulacsi so we needed three very capable goalkeepers. We've brought in Simon Mignolet, who's one of the top young goalkeepers in Europe - he's shown that at Sunderland over the last few years.
"He's got great stature and I think he was player of the season at Sunderland and I really think he can improve on that talent.
"He's part of the Belgian set-up and it's really their golden era of players so him coming here will hopefully increase his opportunities there also."
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