The midfielder is at the Blues on loan for the rest of this season, and there is reportedly an option to make that deal permanent.
Transfer specialist Fabrizio Romano weighed in on the matter this week, suggesting the Blues had agreed a fee if they want to make the Saul signing permanent.
Speaking on his Here We Go Podcast, Romano said: "Let me clarify one thing.
"The clause, the buy option, because it's a loan for €5million (£4.3million) with a buy option.
"It's not €30million (£25.7million) as I see sometimes, it's €40million (£34.2million).
"So, it's €5million loan, €40million buy option. This is the details for the Saul deal."
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