Speaking after his victory at the Welsh Games in Cwmbran in a time of 13.17sec, the 28-year-old Welshman said he was awaiting the results of blood tests following his recent illness.
"I'm now off the antibiotics and I've got four or five races planned against some serious competition," he said. "However, I've lost training time since coming back from Florida and in some ways I've had to go back to the drawing board.
"I'll make a decision on the world championships when I go down to Monte Carlo for my final training camp. If I'm not happy with everything there then I might not defend my title." Jackson is planning to compete in the 100m in next weekend's AAA Championships and trials.
Jackson's Welsh sprint hurdle colleague Paul Gray - last year's Commonwealth Games bronze medallist - crashed into the first barrier, dislocating a finger and fracturing his wrist.
John Regis, in his first home meeting since the resolution of the pay dispute with the British Athletic Federation, could only finish third in the 100m in 10.41sec, behind the winner Darren Campbell (10.34).
Dalton Grant showed his world championship preparations were on course as he high-jumped 2.35 metres to finish third at Eberstadt in Germany. Cuba's Olympic champion, Javier Sotomayor, won with 2.37.
Richard Nerurkar, who will run the world championship marathon for Britain, came second in yesterday's five-mile Bupa Great London run. Christopher Kelong finished a second clear in 22min 41sec.