Dr. Salvador Plasencia can legally reopen his medical practice, Malibu Canyon Urgent Care, as soon as Tuesday -- following his arrest last week -- and his attorney Stefan Sacks tells TMZ ... Plasencia will do just that.

Here's the catch, though, Sacks says the doctor must inform all patients about his ongoing criminal case, and that the feds yanked his DEA registration ... which prevents him from prescribing any meds that include controlled substances, such as ketamine.

As you know, ketamine, a dissociative anesthetic with hallucinogenic effects, is what made Perry go unconscious and drown in his hot tub.

Sacks says Plasencia is still permitted to distribute non-controlled drugs such as antibiotics. What’s more, the patients must give written approval they still want to be treated by Plasencia.

Sacks also told us Dr. Plasencia stopped treating Perry several weeks before his death — and he sees the case against the physician as federal overreach.

Plasencia is one of the 2 physicians charged with illegally conspiring to supply ketamine to the late "Friends" star -- he's pled not guilty while the other doctor, Mark Chavez, cut a plea deal.

Plasencia was released on bond Friday after being accused of supplying Perry's assistant, Kenneth Iwamasa, with several vials of ketamine and showing him how to administer the drug.

Plasencia is also accused of administering ketamine to Matthew.

As for Plasencia allegedly saying, "I wonder how much this moron will pay" in a text about how much he'd charge Matthew for a ketamine delivery ... Sacks says the doctor made an “insensitive” remark or “bad joke.”