According to an article in Sporting Life, Ferrari's engineers are concerned about Kimi Raikkonen's capacity to develop and test their vehicle at the same level Schumacher did during his tenure with the team. Raikkonen will be taking over driving duties for Michael Schumacher, who announced his retirement last week. Although Schumacher has confirmed that he'll be staying with the team for an undisclosed period of time, it was not assumed that the former world champion would fill the test driver position.
Ferrari's chief race engineer, Luca Baldisserri put it best, saying, "After all, driving is the thing [Schumacher] loves most."
[Source: Sporting Life]