Foster has been fined and suspended without pay for the first two games of the regular season for violating the NFL's Conduct and Substances of Abuse polices, the league announced Tuesday afternoon.
The violations stem from a weapons offense and a misdemeanor drug offense, both of which were resolved during the offseason.
"Our organization understands and supports the League's decision," general manager John Lynch said in a statement released by the team. "Although we are disappointed that Reuben will not be with our team for the first two games of the season, we will continue to work with him on making better decisions and eliminating unnecessary distractions. We are encouraged to see Reuben take responsibility for his mistakes, and hopeful that he has learned from them as well."
For his part, Foster held himself accountable for the suspension.
"I accept the League's decision and am sorry that my mistakes have hurt my team," Foster said in a statement released by the team. "I have a responsibility to the 49ers, our fans and our community, and I am committed to learning from this situation and making better choices in the future. The support I have received over the last five months has been humbling, and I do not take it for granted."
He remains eligible to participate in training camp and preseason games before serving the two-game suspension.