Italian newspaper Gazzetta dello Sport claims talks between Chelsea and Inter Milan earlier this week were productive, with the Serie A giants accepting the €15m - potentially rising to €18m - package offered by Chelsea.
The report - carried by Portuguese newspaper A Bola - suggests all that remains is for Guarin to give the green light and sign a contract with Jose Mourinho's side.
Inter Milan are expected to be busy in the January market following the arrival of new owner Erick Thohir. The Indonesian businessman wants to strengthen the squad, and the club have already earmarked PSG attacker Ezequiel Lavezzi as their first major winter signing.
They'll need the money for Guarin first, with the Colombian international likely to feature against AC Milan in the upcoming derby before heading out to London to agree terms on his Chelsea deal during the Serie A winter break.
The report claims the agreement is "almost sealed" with the 27-year-old likely to compete with the likes of John Obi Mikel, Frank Lampard and Ramires for a starting berth in the Chelsea midfield.
He's long been a transfer target for Manchester United, with reports over the summer suggesting David Moyes was keen on the midfielder.
United were thought to be considering a move of their own in January, but it seems like Moyes will have to look elsewhere for reinforcements in the middle of Old Trafford midfield.