Slavia Prague midfielder Tomas Soucek is in London for a medical and further contract negotiations with West Ham.
The 24-year-old was voted as the Czech player of the year and is valued at €20m (£16.8m) by Slavia.
He has 12 goals in 26 appearances this season, two of which came in the Champions League against Inter Milan and Borussia Dortmund.
Soucek won the Czech league and cup double with Slavia Prague last season which ensured him a new five-year contract at the club last summer.
He featured in the Czech Republic team that beat England 2-1 in Prague in a European Qualifier clash in October.
West Ham boss David Moyes said: "I think that he gives us a lot of different aspects, but more importantly he fits the profile of the player I want to bring to West Ham.
"We needed cover for some players, we needed to add another midfield player. We obviously have to add goals. So at the moment he ticks an awful lot of the boxes we were looking to get."
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.