Doncaster said the SPL are investigating this incident, and crowd trouble at the Hibernian v Hearts derby where players were pelted with coins and flares thrown onto the pitch.
The SPL chief executive said: "It's clearly regrettable that a weekend of so much excitement on the pitch has been dominated by reporting of events off the pitch.
Celtic have already apologised for any offence caused and said they had launched an investigation into the incident, which would appear to breach stadium rules forbidding political demonstrations.
The charity Poppy Scotland has also described the banner as "disrespectful".
A section of Celtic fans have long campaigned against the wearing of poppies but Doncaster said it was now an established practice in the SPL for all clubs to wear poppies on their shirts on the weekend of Remembrance Sunday.
He added: "We would welcome the fact that Celtic have moved quickly to apologise for any offence that has been caused. I would also point out that all 12 of the SPL clubs will be wearing poppies on their shirts next weekend in support of Poppy Scotland for the third year in a row."
Doncaster would not be drawn over whether the banner did breach political rules but added: "There have been a number of instances of inappropriate behaviour at games, these incidents do need to be investigated and they are going to be."
"We are currently investigating the matter and, clearly, we apologise for any offence caused."