Mignolet signed from Sunderland in a £9m ($13.9m USD, €10.6m) deal last month, prompting speculation that 30-year-old Reina could be destined for the Anfield exit.
However, Rodgers says Reina was aware of his desire to bring in a new goalkeeper and insists the Spain international still has a future at the club.
"I always felt it was important for us to have competition right the way through the squad, and that includes the goalkeepers," Rodgers 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 (who has joined Red Bull Salzburg), 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 has been granted extra time to recover after representing Spain at the 2013 FIFA Confederations Cup in Brazil, but he is expected to link up with the squad for their pre-season tour matches in Australia and Thailand.
Speaking prior to the completion of Mignolet's transfer, Reina said he welcomed the Belgian's arrival.
"Every team needs competition, and when it's a positive one, it's more than welcome," he said.
"If it's finally done, I'm here to welcome him. Anything he needs, I'm here."