Chelsea's Fran Kirby is in the form of her life ahead of Sunday's crunch WSL clash

The 2020 WSL summer transfer window was sheer wonderful carnage.

We thought it was quite exciting when Manchester City signed Chloe Kelly in July - and then the chaos unfolded.

We had World Cup champions, Olympic gold medalists and Champions League winners descending upon the league, the transfer record was broken, Lucy Bronze came back and to top it all off, Alex Morgan spontaneously joined Tottenham.

But while everyone was getting excited about their various new recruits, Chelsea had someone who had been at the club for half a decade, but come the start of the 2020/21 season was going to feel like a brand new signing.

Fran Kirby - once the short-haired, diminutive future of English football after she burst onto the scene at the 2015 World Cup despite playing for Championship outfit Reading - had featured just four times for the Blues during the previous campaign.

Kirby was diagnosed with pericarditis - an inflammation of the lining around the heart - in November and admitted she came close to throwing in the towel and turning her back on the game. She missed the rest of the season, but Chelsea coped in her absence and won the WSL title.

Their already eye-watering forward line had seen the addition of Sam Kerr in January and then Pernille Harder in the summer - two of the finest players in world football. It could have been easy to forget about Kirby.

But despite going nine months without kicking a ball competitively, the 27-year-old hit the ground running this term. In the Community Shield at the end of August, neither Chelsea nor City had played since February. Kirby hadn't played since November. Yet she looked the sharpest player on the pitch.

Her performance was a sign of things to come. The England international has operated out wide for large parts of the season, where her intricate link-up play, vision and ability to provide for her teammates have really shone through.

Against Reading in Chelsea's most recent WSL outing, Kirby was deployed in the number ten role - a position she has frequently occupied for the Lionesses - and took centre stage.

The forward scored four times (including two headers despite being 157cm tall) in a devastating attacking performance. Her cohesion with Kerr was electric, she pounced on any let up in the Reading backline and was razor-sharp in front of goal as the Blues ran out 5-0 winners.

Chelsea face Manchester United on Sunday as the WSL's last remaining unbeaten sides go head to head. United have hardly put a foot wrong this term, but with Kirby in the form of their life, their unbeaten record will come under threat.