United boss Sir Alex Ferguson has responded to intense speculation over Rooney's future by insisting the England striker will still be at Old Trafford next season.
But Mancini was still asked whether he might be tempted to test United's resolve over the 27-year-old, and he replied: "I think that Rooney is one of the best strikers in Europe but I think it is difficult he can leave Man United - I don't think (so)."
Suggestions Rooney could leave United have gathered pace since he was omitted from United's starting line-up for their Champions League loss to Real Madrid on Tuesday.
Mancini says he would be surprised if something such as that led to his departure.
The Italian said: "I don't know. I don't know this situation. I can understand maybe Rooney would be upset if he didn't play but these are things that can happen in every team. After one week it is finished."
There has been a report suggesting City striker Edin Dzeko could hold the key to Rooney's future at United.
Dzeko has been linked with a return to German football with Borussia Dortmund, whose star striker Robert Lewandowski is reportedly coveted by United. Were Dzeko, signed from Wolfsburg for £27million two years ago to move on, that could tempt Dortmund to cash in on Lewandowski 12 months before his contract expires.
But Dzeko, City's top scorer in the Premier League this season with 12 goals, has often stated his desire to remain at the Etihad Stadium and Mancini claims not to be aware of any interest.
He said: "At the moment, there is nothing. In the end, maybe, I don't know. In the summer, it could be possible. Dzeko player is an important player for us. We want that he stays here."
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