Felipe Massa's inconsistent race finishes cost him his place in the Ferrari team, says the company's president Luca Di Montezemolo.
He said Massa was an "exceptional guy and a wonderful person", but added: "In 2012, we felt the lack of his points in the constructors' [championship]."
And Fernando Alonso was kept informed about the choice of new team-mate Kimi Raikkonen, according to the Italian.
Classic F1 - Raikkonen wins 2007 title
"Alonso is the first to be happy that he is coming here," he said.
Last week, Ferrari confirmed Lotus driver
Raikkonen had agreed a two-year contract,
starting from next season.
won the world title with Ferrari in 2007
but was displaced by the arrival of
Spaniard Alonso in 2010.
Di Montezemolo, who took the decision to replace Brazilian Massa with Raikkonen following the
Italian Grand Prix,
said: "The relationship [with Felipe] was clear. He needed results and so did we.
"He did get some, but he was inconsistent, having some good races but not on a regular basis. It will be good for him to have a change of scenery."
It is not clear where 32-year-old Massa's future lies, but he is being linked with the 2014 Lotus seat vacated by Raikkonen.
Ferrari's decision to partner Alonso, 32, with the Finn signals a return to the policy last employed between 2007 and 2009, when Raikkonen and Massa competed on equal terms.
Either side of that period, with Michael Schumacher from 1996-2006 and then with Alonso for the past four years, there has been a clear number one driver.
Fernando Alonso one of the best - Di Montezemolo
Speaking about suggestions Alonso was not informed of Raikkonen's arrival, Di Montezemolo added in
Gazzetta dello Sport:
"We are not masochistic enough to take on a driver without informing Alonso.
"Fernando was always in the picture regarding the choice, taken partly because employing a youngster, in what will be a complex 2014 season, did not inspire confidence.
"In a nutshell, I wanted a driver who would not make me regret Massa [leaving]. What I ask of Raikkonen is wins, a consistent performance level and podiums and Alonso will be the first to benefit."
Singapore Grand Prix, day one
- Friday 20 September: First practice at 10:55 BST on BBC Radio 5 live sports extra, plus live text commentary online from 10.30. Second practice at 14:25 BST on BBC Radio 5 live sports extra, plus live text commentary online from 14:00.
Singapore Grand Prix, day two
- Saturday 21 September : Final practice: online live text commentary from 10:30 BST. Qualifying at 14:15 BST on BBC Radio 5 live sports extra plus live text commentary online. Qualifying highlights, 17:15 BST on BBC One.
Singapore Grand Prix, day three
- Sunday 22 September: Race coverage at 13:00 BST on BBC Radio 5 live, and live text commentary online from 12:00. Race highlights, 17:00 BST on BBC One.