The midfielder joined the Baggies on a season-long loan deal last week after signing a new five-year contract at Stamford Bridge.
Not involved in the 5-2 loss away at Everton at the weekend, the 20-year-old was handed a spot in Albion’s starting XI for their clash with Championship outfit Brentford in the Carabao Cup.
And he wasn’t the only player with a Chelsea link in the West Brom starting XI.
Blues legend Branislav Ivanovic was also making his debut for Slaven Bilic’s side after joining the Midlands club on a one-year deal.
Seeing the pair in the same team garnered a huge reaction from Chelsea supporters – with one in particular claiming it was ‘Legend and future legend’ starting against Brentford.
Click here for the best responses.
However, it turned out to be a disappointing night for Gallagher and Ivanovic as West Brom were dumped out of the competition at the third-round stage on penalties.
Although, as spotted by Chelsea fans on Reddit, Gallagher is rather confident from the spot.
Take a look at the penalty which was uploaded to Twitter by @willreyner.
Although it has sparked a debate over whether the effort can be classed as a panenka or not.
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One fan said: “Hardly a panenka, barely came off the ground.”
Which prompted a defence of Gallagher’s effort: “Panenka was never about the technique,” another fan said.
“The keeper thought he was going to smash it, meaning he would’ve had to act early,” is the comment that may have settled the debate.