The 50-year old Scotsman was removed from his post at Old Trafford on Tuesday morning after just 10 months in the job and the manner of his dismissal has been met with derision by the LMA.
"We are very disappointed with the nature of David's departure from Manchester United and to read extensive reports in the press, confirming David's sacking, before David himself had been spoken to officially by the club," read the LMA statement.
"Throughout his time at United, David, as he always does, has conducted himself with integrity and professionalism, values that he believes in and that have been strongly associated with the club and its rich tradition.
"It is therefore sad to see the end of David's tenure at United being handled in an unprofessional manner."
However, United have hit back at the claims which were in relation to reports emerging on the internet on Monday night before the Red Devils board had decided on the future of the former Everton boss.
"We do not accept that it was handled in an unprofessional manner," read the United statement.
"The decision was not taken until late Monday night and was communicated face-to-face first thing on Tuesday morning.
"When reports started emerging on internet news sites on Monday afternoon, no decision had been taken at that time."
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