Arsenal have complete the signing of 17-year-old midfielder Krystian Bielik after agreeing terms with Legia Warsaw, the Premier League giants confirmed.
Manager Arsene Wenger had already announced the arrival of the Polish starlet last week in a deal worth around £2m, claiming he will go straight into the first-team squad despite his age.
"He's a defensive midfielder, 6ft 2ins, he has a good energy level and technical level. Also, it's a gamble. But on what we saw it's worth taking," Wenger said.
"It's less than £2m. It's an awful lot of money for a player if he doesn't succeed. If he does succeed then it's cheap. Yes [he will go into the first-team squad]."
Bielik is expected to back-up Francis Coquelin and Mathieu Flamini in the second part of the season, and he has been earmarked as the long-term replacement for Mikel Arteta, whose future at the Emirates Stadium is still uncertain, with his contract due to expire in the summer.
The north London side have now confirmed their first January signing through an official statement "subject to the completion of regulatory processes".
"Arsenal have completed the signing of 17-year-old midfielder Krystian Bielik from Legia Warsaw for an undisclosed fee," the club said.
"Bielik made his senior debut for the Polish club in August, aged 16. He went on to feature five times for Legia in the league and once in the Europa League."
The Gunners had been monitoring the starlet's development for a while after he spent some time on trial at the club's London Colney training ground in November.
Bielik recently claimed he also had an offer from Hamburg but wanted to move to the Emirates Stadium to work under the Arsenal manager.
"First of all, because of Arsene Wenger. He is a legend, 'The Boss' as they call him at Arsenal," Bielik said.
"In Hamburg, the team has a very young coach and their target for this season is to avoid the relegation from Bundesliga. This also had an impact.
"Certainly it will be harder for me to get through at Arsenal. But if I succeed in three or four years, I will be at the footballing top. After all, this is one of the best clubs in Europe and certainly better than Hamburg."