If this were to happen, I doubt it'd happen before we play them, regardless of what we offer. No way Pep would strengthen us just before we play each other.
Technically it's possible to sign him before we play them. Like, 12 hours before we play them, making him ineligible for the match Which is what we tried to do when selling Sissoko to Watford, but apparently somebody didn't check the kickoff time and he played against us...