Chelsea are understood to have inserted a clause into the £90m Kai Havertz deal which involves them winning the Champions League.
The Blues are believed to be on the brink of signing Bayer Leverkusen playmaker Havertz as Frank Lampard continues to tinker with his squad.
Stamford Bridge director Marina Granovskaia has been negotiating with Leverkusen for weeks.
And she is understood to have finally reached an £89m agreement with the Bundesliga side, with talks concluding on Wednesday.
The initial fee is thought to be £72m, with a number of add-ons potentially taking it up closer to the £90m mark.
According to the Mirror, one of those will depend on whether he helps Chelsea to win the Champions League over the next five years.
Leverkusen boss Peter Bosz admitted earlier this week that his star man would probably not train with the Bundesliga side again.
“Unfortunately our squad isn't set yet. I don't expect Havertz to train with us again,” he said.
“It's possible more players will transfer. We definitely still have to add some players.”
The fee takes the Blues’ summer spending well above £200m, having already snapped up another six players who will all be sniffing around the starting XI.
Lampard’s first signing was Ajax winger Hakim Ziyech, who cost a relatively risk free £37m.
Get the latest transfer news straight into your inbox!
Want to be on the ball with all of the latest football news?
Well then sign up for the brilliant new Daily Star Sport email newsletter!
From the latest transfer news to the agenda-setting stories, get it all in your email inbox.
How do you sign up?
It only takes a matter of seconds.
Simply type your email address into the box at the top of this article and hit 'subscribe'.
And that's it, job done. You'll receive an email with all of the top news stories every single morning.
You can find out more information on our email newsletter on this link here.
He was followed through the door by top German striker Timo Werner, joining from RB Leipzig for £47.5m.
Chelsea have also tied down Leicester left-back and long-term target Ben Chilwell for £50m.
And finally joining on free transfers, centre-backs Thiago Silva and Malang Sarr arrive from playing regularly in France last year.