West Ham have confirmed the loan signing of Czech midfielder Tomas Soucek from Slavia Prague.
The Hammers also have the option to sign the 24-year-old permanently at the end of the 2019/20 campaign when his contract at his parent club expires.
Soucek arrived in London on Tuesday to undergo his medical and for final negotiations between the two clubs, and he has now completed a loan switch to the London Stadium.
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The midfielder, who has made 26 appearances and scored 12 goals in all competitions for Slavia Prague this season, is a two-time Czech top-flight winner and has international 25 caps.
Last season, his 18 goals from midfield helped Slavia win the Czech league and cup double, and he was also named the Czech First League Player of the Year in 2018/19.
He operates predominantly as a central defensive midfielder but can also deputise at centre-back, offering strength and height to Moyes' midfield options with his 6ft 4ins frame.
West Ham boss David Moyes said: "We are delighted to welcome Tomas to West Ham United.
"I think that he gives us a lot of different qualities, but most importantly he fits the profile of the player we want to bring to the club. He is young and hungry but with an established pedigree and proven talent.
"He was captain of Slavia Prague, he's played as a defensive midfielder but he's scored a lot of goals as an attacking midfielder as well.
"At the moment he ticks a lot of boxes. We need to give him the opportunity and time to settle in but we are confident he will prove to be a strong addition to the squad."
Soucek becomes Moyes' second acquisition of the January transfer window, with Darren Randolph also having also joined the club from Middlesbrough for an undisclosed fee.
Meanwhile, ahead of the transfer deadline on Friday, the Hammers have had an initial loan offer for USA international centre-back Aaron Long rejected by New York Red Bulls.
West Ham, who face Liverpool in the Premier League on Wednesday, have yet to confirm whether Soucek will be ready to join up with the squad in time to face Brighton in the top flight on February 1.
How to follow the January transfer window with Sky Sports
Sky Sports will bring you the very latest news from the January transfer market with the return of three shows.
Start your day with Good Morning Transfers at 9am as our team of reporters bring you the latest news and insight. Transfer Talk then follows at midday delivering analysis of the biggest stories. Then join us at 7pm for the definitive round-up of the day's news with The Transfer Show.
Meanwhile, the Transfer Talk podcast will also be back at the turn of the year with more expert analysis from here and across the continent.
And as well as tuning into Sky Sports News, don't miss a thing with our dedicated Transfer Centre blog.