"I've had physical tests and I'm confident I will come back faster, stronger and fitter than I ever was," Collymore told The Mirror.
The 35-year-old former Liverpool and Aston Villa forward - who flew to Tenerife earlier this week to embark on a three-week fitness programme - estimates that given a month he will be back to his best.
"A month from today, I guarantee I will be able to stand side by side with any striker in the country and my physique will be up there with any of them," Collymore added.
Robben slams Chelsea offer
"This time I'm not going to self-destruct. You are not going to see headlines about me being kicked out of a bar somewhere in the early hours rolling drunk.
"l know I can still be among the best."
Euroscout - Kevin Prince Boateng
Hammers agree Dyer fee