Presenter Ortis Deley has been sidelined by Channel 4 bosses after apparently struggling to read scripts and name his co-hosts while fronting the athletics coverage.
Deley, a children's presenter who has also fronted Channel 5's The Gadget Show, has now been replaced as the main anchor by Rick Edwards.
The channel said today that his role had been "scaled back" although he will continue to feature in the IAAF World Championships programmes.
Since the competition began at the weekend, viewers have seen his stilted delivery as he repeatedly had to refer to his printed script. He also had to correct himself frequently when he misread his lines and failed to get his tongue around the names of fellow presenters.
At one stage he told viewers they would see "history in the making as Oscar Pistorius from South Africa makes history".
A video of many of his appearances in Daegu, South Korea, has been placed on YouTube accompanied by comments blaming Channel 4 for putting him in the spotlight.
One said: "Putting a kids TV presenter in charge of the biggest sporting event of the year?! Only God? knows what Channel 4 were thinking."
Another wrote: "The bosses at Channel Four have to take all the blame for this embarrassment. This is a very big event for them and they should've made sure they hired a half-decent presenter who could handle live TV."
A spokeswoman for the station said: "Channel 4 is committed to developing new presenting talent and this extends to our coverage of sporting events.
"Ortis Deley's role in Korea covering the world athletics has been scaled back but he will continue to be on air for the duration of the competition.
"In total we have a team of 10 commentators covering this event, from Michael Johnson and well-loved British athletes Dean Macey, Katherine Merry and Iwan Thomas to new presenters."
C4 landed the rights for the IAAF World Athletics Championships from the BBC, which had broadcast the event for 27 years.
The broadcaster said it has also responded to viewer feedback by shortening ad breaks to allow the action to flow and ensure the coverage is not interrupted at vital points.