The Celtic midfielder had a strong comment for a Hearts player on Sunday.
Celtic new boy Scott Sinclair came off the bench to net a late winner and seal a dream debut for the Hoops following his switch from Aston Villa just hours earlier.
There was a moment of controversy in the first half when Jamie Walker went down in the penalty area under a challenge from Kieran Tierney, before scoring the resulting penalty to cancel out James Forrest's eighth-minute opener.
Afterwards, the Celtic skipper labelled Walker a "cheat" and quipped that his 'diving' was better suited to the springboards at the Rio Olympics rather than Tynecastle.
And Nielsen admitted that he was disappointed to see Brown speak in such a way about a fellow professional footballer.
“It’s disappointing when you hear fellow professionals saying things like that but Scott’s entitled to his opinion," he told The Scotsman.
“But from our perspective, Jamie has said there was contact there. If there’s contact, it’s up to the referee to make a decision. At no point did Jamie claim for a penalty, as any of our players did. The referee makes the decision and you have to accept it.”
Celtic boss Brendan Rodgers told The Daily Record today that he was building a dossier on every referee in Scottish football to analyse them and their decisions.
It did look a harsh decision when John Beaton pointed to the spot on Sunday, but it also perhaps a futile exercise to complain about diving in the modern game, given its incidence.