Morgan, perhaps the most easily recognised UK newspaper editor thanks to his many appearances on national TV, was sacked by the Trinity Mirror chief executive, Sly Bailey, last week over the publication of fake pictures purporting to show UK troops abusing Iraqi prisoners.
Ian Tournes, the press director at Starcom MediaVest, said: "Morgan has done a lot for the Mirror. He's the most famous newspaper editor and a great self-publicist and has helped to get readers to pick up the paper."
Jane Wolfson, the non-broadcast director at Initiative, said: "His departure is a loss but you can get to a situation where the editor becomes bigger than the paper. That happened a little with the Mirror's anti-war policy."
Morgan was fired last Friday, after he had lost the confidence of the Trinity Mirror board following the newspaper's publication of the fake pictures. Des Kelly, previously the deputy editor, was appointed as the acting editor.
A statement from Trinity Mirror said: "The Daily Mirror published in good faith photographs which it absolutely believed were genuine images of British soldiers abusing an Iraqi prisoner. However, there is now sufficient evidence to suggest that these pictures are fakes and that the Daily Mirror has been the subject of a calculated and malicious hoax."
It added: "It would be inappropriate for Piers Morgan to continue in his role as editor of the Daily Mirror and he will therefore be stepping down with immediate effect."
Reports have suggested that frontrunners to replace Morgan, along with Kelly, are The People editor, Mark Thomas, and Phil Hall, the former News of the World editor. News International will also be concerned that the Mirror may consider the News of the World editor, Andy Coulson.
During almost nine years as the editor of the Mirror, Morgan, 39, was unable to address its falling circulation despite recent exclusives such as Paul Burrell's diary and its "Royal Footman" story. Its April 2004 sales were down 2 per cent to 1,888,145. He also attracted criticism for the title's anti-war stance.
Tournes said that the Mirror might face a backlash from readers over the Iraq story: "I wouldn't think clients will stop spending because of this, but some readers will be thinking negatively and may consider other papers."
As for the future, Wolfson said: "An editor who is more open to the needs of advertisers would be good from an advertiser view, but in terms of marketing to readers it needs to be more objective."
Alison Wright, the managing director of Manning Gottlieb OMD, said: "It's important for advertisers that it sorts itself out, to make sure that The Sun has some decent competition."