The 26-year-old Olympic champion, from Leeds, who won the world series in 2009 and 2011, came home third in the latest leg of the 2014 season in Hyde Park.
His younger brother Jonny trailed home in fifth in the sprint distance event as the two of them, and series leader and defending champion Javier Gomez, were outsprinted by Spain’s Mario Mola, who pipped South Africa’s Richard Murray at the line.
“This is most likely the end of my world series,” said Brownlee, whose performances this year have been affected by injuries that meant he was unable to build a base of fitness over the winter.
His admission does not come as too great a surprise. The London leg was only his second appearance out of four races this season.
With four to go, he would have to race each one to comply with the governing body’s rules that stipulate world championship competitors contest six of the eight races, including the grand final in Edmonton in September.
That looked unlikely for Brownlee even before the weekend’s result as the next two races – Chicago and Hamburg – come when he and his brother plan to be training at high altitude ahead of the Commonwealth Games.
The Leeds siblings have already highlighted the Games in Glasgow – when they will race against each other in the individual event on July 24 and together representing England in the team event two days later – as their priority for the year.
Jonny Brownlee is still in the hunt for what would be a second world title despite finishing outside the podium places for the second world series event running.
His two second-place finishes in Auckland and Cape Town mean he is still second in the overall standings.
Jonny, who was the last world sprint champion in 2011, said of the shortened track: “It was very tough to run.
“Normally you get down to a group of four or five very quickly, but the whole way round there was a big group. The pace was fast.”
Alistair, who appeared to almost take a wrong turn entering the final straight, said: “I was just going as hard as I could for that last kilometre, trying to put in attack after attack, but it wasn’t good enough. They were still faster than me.
“I went as hard as I could. I thought that was the best thing to do but 100-80 metres to go I just had nothing left.”