Reina has been linked with a return to his 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 has dismissed suggestions Mignolet 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."
Reina appeared to be being lined up as the long-term successor to Victor Valdes at the Nou Camp but his compatriot has insisted he will see out the remainder of his contract with the Catalan club before seeking a new challenge.
With no approach made to Liverpool for their Spanish goalkeeper it is expected he will rejoin his team-mates for their summer tour matches in Australia (July 24) and Thailand (July 28).
While most of the squad returned to pre-season training this week, those involved in the Confederations Cup in Brazil - Reina and Uruguay duo Luis Suarez and Sebastian Coates - have been given additional time.
Liverpool's opponents in Australia are Melbourne Victory and coach Ange Postecoglou, as a childhood Reds fan, is eagerly awaiting their visit.
"Growing up in Australia, the old English first division was the one we used to watch on our TV sets," he said. "It wasn't just the fact Liverpool were successful in the 1970s and 1980s. It was the stories behind that.
"From the Shankly era, I gained an attachment to the club and an attachment to coaching from there.
"It will be a massive thrill for me to be able to coach against them."
Postecoglou has been impressed with the work Rodgers has done in his first year in charge.
"He is trying to change the way they play a little bit. He is changing the playing roster and getting them to play in a specific way," he added.
"I am trying to do similar things at Melbourne Victory. I have been here a year, as he has been at Liverpool.
"He has to contend with a much bigger tradition and history in the game but we are facing similar challenges and if I get a spare moment I would love to sit down with him and get an insight into what he is going through and what his plans are."