The 30-year-old Yorkshireman, who won Olympic gold at London 2012 and Rio 2016, is renowned as one of the strongest finishers around, but in Glasgow he was left treading water as France’s Pierre Le Corre burst clear to take gold.
Spain’s Fernando Alarza won silver and Belgium’s Marten van Riel the bronze with Leeds’s Brownlee a distant fourth at Strathclyde Country Park.
With the Tokyo Olympics just two years away, Brownlee has to decide whether he wants to commit to defending his title.
He says he will take some time off at the end of an injury-ravaged season.
“There have been times when I have questioned whether I want to carry on doing it. To be honest I just enjoyed racing [yesterday],” he said.
“It is tough when you have had injury after injury after injury and training has just been really hard. It just is fantastic to be here.
“I got really beat up in the first 100m and I had a lot of swimming to do to make it up and I did that. Small things like that you can take pleasure from.
“I knew I was going to struggle on the run as I’ve not done enough sessions yet, but I enjoy racing. I have six weeks left of races and I will do them. After that we will see.”
Brownlee looked strong after emerging from the swim in the leading pack. He maintained his position in a breakaway group of nine during the cycle phase, and went clear with Le Corre and Marten Van Riel – who finished third – until his lack of recent training miles visibly began to take its toll.