Sanches signed for the German giants for a fee of €35 million from Benfica.
The 18-year-old made just 35 appearances for the Portuguese side's first-team and Rummenigge admitted that he is not sure whether signing Sanches will work out.
Of course, transfers like that are always a bit of a gamble," he told 'TZ'.
"But all clubs are on the lookout for players like them.
"Had we not made a move for Sanches this early, we would not have stood a chance after the Euros. I am very happy that we had the courage to spend €35m on what was already an expensive deal.
"He is a player who has a lot of personality and power for someone his age. I hope we will bring us a lot of joy".
Do you think Sanches will prove to be a success at Bayern?