The LMA chief executive, John Barnwell, admitted Rennie's decision to send off Alan Shearer looked "very harsh", but he criticised Gullit's angry reaction after the Magpies' 1-0 defeat by Aston Villa.
"It was very unfortunate on the first day of the new season and it's something we don't want repeated," said Barnwell. "The Association has noted Ruud Gullit's remarks, and we don't want to prejudge the issue of Alan Shearer's dismissal until we see the referee's report.
"Having seen the video evidence, however, it would appear it was a harsh decision, and therefore I can perhaps understand Ruud's reaction. Managers up and down the country will sympathise with him. But we have responsibilities to maintain a working relationship with referees and we don't condone the extreme nature of Ruud's comments.
"We do understand his frustrations. But there is a mechanism in place for lodging complaints, and we always urge our managers to use it. There are procedures in place, and if they are not correct we should be attempting to change them."
The Football Association is still awaiting Rennie's report.