The 21-year-old midfielder is enjoying preseason with the Blues after returning from a loan spell with West Bromwich Albion.
"It's great to be back," Gallagher told the club's website.
"I'm enjoying seeing some old friends who I've grown up with through the Academy and to train under the manager has obviously been great as well.
"The sessions have been tough but really good so I've enjoyed the first few days."
And Gallagher added that he is already improving his game by playing with some of Chelsea's biggest stars.
"You always want to work with the best and obviously there's some great players here in training,' he said.
"That only helps me improve, to train with such good players. Even though it's only been a few days so far, I feel like it's helped me a lot so that's been good."
It remains unclear if Gallagher will remain at the club beyond this summer.
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