World champion James Magnussen is not willing to write off Ian Thorpe but has questioned whether the Olympic great has left himself enough time to make a success of his London comeback bid.

Thorpe, 29, is putting the final touches on his preparations for next month’s Olympic trials in Adelaide, where he will attempt to win a spot on his first Games team since Athens 2004.

The five-time Olympic gold medallist’s performances since returning to competition in November have left many predicting he will fail in his ambitious comeback bid.

And while 100m freestyle world champion Magnussen still considers him an outside chance of winning a relay spot in the 100m or 200m freestyle, he admits time is not on Thorpe’s side.

“I think it would have to be said that it’s proved a lot more difficult than everybody first thought,” Magnussen said of Thorpe’s comeback on Thursday.

“I’m certainly not going to discount him before the Olympic trials but it has proved an uphill battle for him so far.”

Asked to compare the comebacks of Thorpe and Geoff Huegill, who shed more than 45kg to win gold at the 2010 Delhi Commonwealth Games, Magnussen was frank.

“I think the thing with Geoff was he gave himself plenty of time and set realistic goals along the way,” Magnussen said.

“I think he gave himself more time to get back to where he needed to be and he’s also coming back to an event that he’s familiar with.

“He was always a great 100m butterfly swimmer and to come back into that event was a little bit more natural I feel, whereas Thorpe’s gone from a 400m swimmer but is trying to come back as a 100m sprinter.

“Speed is a hard thing to attain.”

While Magnussen is a virtual certainty in Australia’s 4x100m freestyle relay team, he is excited about the depth in the fight for the three remaining places in the team for London.

“To have guys like Michael Klim and Ian Thorpe and guys like myself who’ve now established themselves in international competition and young guys like Cameron McEvoy coming through, it’s going to give the race (at trials) great theatre,” he said.