McFarlane stepped in twice as interim manager this season following the sackings of Liam Rosenior and Enzo Maresca respectively, leading the side to a creditable FA Cup final performance before the 1-0 defeat to Manchester City at Wembley.
Set-piece coach Bernardo Cueva and head of goalkeeping Ben Roberts are also expected to remain as part of the new setup. Alonso will additionally bring four members of his own trusted staff from his time at Bayer Leverkusen and Real Madrid: assistants Sebastián Parrilla, Alberto Encinas and Beñat Labaien, and fitness coach Ismael Camenforte López.
McFarlane declined to go into detail about the content of his exchange with Alonso, but was visibly excited about what lies ahead.
"He sent me a text message yesterday. I'll keep that private, but mainly just around the final. I've had a brief conversation with him via text. Really exciting news. Very talented, massive pedigree. Really excited for the club. We're all looking forward to working with him."
He refused to be drawn on his own specific role under Alonso, saying his focus remains entirely on the final two Premier League matches against Tottenham and Sunderland.
"I haven't thought about that. There is so much to prepare for. There is so much to play for and answer. But my focus is always on the next game and the next training session."
McFarlane also reflected on what Chelsea's young squad has shown this season despite the inconsistency of results.
"Even though it's a disappointing season, they are showing at times this year the kind of quality that we have. It's a massive club and it will always attract top players and top managers."
Alonso officially begins his tenure on July 1.