West Ham are in negotiations to sign CSKA Moscow's £25m-rated playmaker Nikola Vlasic.
The Croatia international, 23, has been earmarked by manager David Moyes as another creative addition to his squad.
West Ham are optimistic of a deal being completed before Tuesday's 23:00 BST transfer deadline.
That deal could mean the end of their hopes of getting Jesse Lingard back to London Stadium after an impressive spell on loan from Manchester United.
Lingard, having fallen out of favour at Old Trafford, scored nine goals in 16 games after joining the Hammers on loan last January, earning a recall to the England squad in March, although he did not make the final squad for Euro 2020, and was instead on standby.