Porzingis missed Dallas' scrimmage on Sunday because of his forgetfulness.
"He didn't get tested; just forgot to get tested. [So] when that happens, for safety reasons, he's unable to join the team the following day," Mavs coach Rick Carlisle said in a statement. "He's getting re-tested today and I believe he'll be able to re-join us tomorrow."
Information from The Associated Press was used in this report.