Anthony Joshua has warned Deontay Wilder and Tyson Fury they risk facing a better version of him if frustrating fight negotiations drag on.
Unified world heavyweight champion, Joshua, faces Andy Ruiz Jnr., on June 1.
The 29-year-old says the bout will showcase evolving methods he began to use after beating Wladimir Klitschko.
“I’ve got through with strength, guts and heart,” said Joshua. “I’ve got away with mistakes. I realised I couldn’t continue my journey like that.”
Speaking to BBC Radio 5 Live boxing, Joshua added, “After Klitschko, I thought ‘how many more fights can I have like that before the mistakes aren’t there anymore?’
“For the last two years, hand on heart, with my team, we spend so much time doing things outside of boxing, things that can drain me.
“How do we now train smart to become smarter in the ring? Less quantity, more quality. It didn’t happen overnight. It has taken two years to implement it and this is the first camp we are really seeing it.
“Look at my last fight against Alexander Povektin. I was ill, tired, had a flu, had a headache. I was going through changes. It will be interesting as this is the first time I can express these things.
“The longer Wilder and Fury leave it, the tougher it will be for them as I am not the fighter of two years ago. Give me another year or two and I’ll develop that little bit more.”
Joshua was complimentary of both Fury and WBC Champion, Wilder’s, displays in their December draw, but BBC Radio 5 Live boxing analyst Steve Bunce believes the assertion he will improve in coming years is a “subtle way to tell them to get to the negotiating table.”