The manager says the Spaniard was aware of his plans to bring in competition for the No.1 jersey and feels a weekly battle can only be positive
The Belgian international’s €10.5 million transfer raised some question marks over Reina's position at Anfield, despite assurances from both the Spaniard and his manager that his future remains on Merseyside.
Mignolet also faces the challenge of displacing Chelsea goalkeeper Thibaut Courtois for Belgium, and Rodgers feels a weekly battle for the No.1 jersey can only be positive for player and club alike.
"I always felt it was important for us to have competition right the way through the squad, and that includes the goalkeepers," Rodgers told Sky Sports.
"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 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 recently been linked with a return to Barcelona, where he came through the youth ranks before moving to Villarreal in 2002.