The FCB director has insisted that the reigning German champions champions must keep building for the future in order to remain competitive at the highest level
The Bavarians announced the signing of the Poland international on a five-year-deal upon the expiration of his contract at the end of this season.
Many have claimed that the Bavarians do not need the striker as they already have plenty of high-profile options in attack, yet Sammer has stressed that it's vital for Bayern to always prepare for the future.
"Mario remains a key player for us. However, he has to accept - like the rest of the squad - that there will always be stiff competition for places," Sammer was quoted as saying by Bild.
"Bayern cannot afford to get complacent and sit back, relax and be satisfied with our current squad.
"We cannot just wait until things eventually fall apart and then be forced to panic-buy.
"Our transfer policy is stable and sustainable. Why would it be a bad thing if we sign players from other Bundesliga clubs? People could also show us some respect and acknowledge that we are doing our job."
Lewandowski, 25, has signed a contract until the summer of 2019 with Bayern and will join his new club on a free transfer at the end of the 2013-14 campaign.