Arsenal have confirmed that Willock has signed on, although have not stated for how long.
The 20-year-old had a strong pre-season for the Gunners, earning him three appearences in four of their Premier League games so far.
Willock has been associated with the club since he was four years old, and has reiterated that north London is where he wants to be.
"It's right in my heart and mind... this is the club for me," he told Arsenal Player."
Arsenal head coach Unai Emery also commented on the contract extension, highlighting how well Willock has developed.
“Joe has progressed a lot in the last year. He is technically strong and has shown the confidence to take responsibility and play his game whatever the occasion or opposition," the Spaniard said.
"I’m looking forward to working with to help him develop further and fulfil his potential.”
Willock was linked with Bayern Munich toward the end of the summer transfer window.
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