Palmer has scored nine Premier League goals this season — five from the penalty spot — with one assist and 22 chances created, numbers significantly below the levels he set in his first two seasons at the club.
He has missed 21 matches in total, the bulk of them with a chronic groin condition, pubalgia, that left him unable to sprint or shoot at full capacity when he forced himself to play on through the problem earlier in the campaign. His World Cup place with England is under real pressure, with Thomas Tuchel having warned him about fitness during the March international break.
Speaking ahead of Monday's home game against Nottingham Forest — a match Chelsea need to win for their European qualification push — McFarlane was emphatic in his defence.
"It's been a difficult period for Cole. He's had his first injury that he's pretty much ever had in his career and he's had to learn how to deal with that."
He rejected the premise that Palmer's quality has dropped.
"I don't agree with the narrative that he isn't playing well. There are obviously games where he can impact more, but there have also been a lot of occasions where he's created a lot of good chances for players. He can't control whether that's finished."
On the path back to his best, McFarlane was patient but clear.
"It's just a case of building that consistency. I'm really pleased with Cole. He shows us his talent every single day, his energy and his enthusiasm to play. He's still a top, top player, one of the best in the world. I have no concerns over Cole being ready to impact games from now to the end of the season, and hopefully in the World Cup, in big moments for England."
His directional comparison to Palmer's youth career — McFarlane previously worked in Manchester City's academy and watched the player as a teenager — was telling.
"He sees things that other people don't see. He is just doing it at a higher level against a higher level of opposition, but very much the same type of player."
Palmer faces a direct head-to-head test of England credibility on Monday, with Nottingham Forest's Morgan Gibbs-White — joint Premier League top scorer since January with ten goals — arriving at Stamford Bridge in the form of his life.
Tuchel is believed to have a shortlist of No.10 candidates that includes Palmer, Gibbs-White, Jude Bellingham and Morgan Rogers, with the final squad announcement approaching quickly.