The Brazilian rued picking up the knock, but is determined to recover before die Roten kick off their campaign with the short trip to Greuther Furth on August 25
The 26-year-old suffered the knock during Friday's 3-2 friendly defeat to Napoli, and is expected to face around a month on the sidelines.
Die Roten kick off their campaign with the short trip to Greuther Furth on August 25, and the Brazilian is determined to regain his fitness as soon as possible.
"I am very sad about this injury," he told Goal.com. "I played through the entire preparation camp and I got injured on the last day. I was in good shape physically.
"Now I have to rest completely for the first 10 days and then I have to undergo physiotherapy. I can't wait to return to fitness and be able to help my team-mates.
"Depending on the recovery process, I can come back for the start of the league."
Rafinha was a €5.5 million signing from Genoa last summer, but lost his place in the Bayern first team after a poor run of form.
David Alaba also suffered an injury during the match with Walter Mazzarri's men, and will be missing for around eight weeks with a stress fracture in his foot.