West Ham are to make an improved bid for Eintracht Frankfurt winger Filip Kostic after their initial £12m plus a £3m in bonuses was rejected.
Manager David Moyes remains hopeful of persuading the 29-year-old to join.
Kostic experienced a successful campaign last season, scoring seven goals in 43 appearances in all competitions as Frankfurt won the Europa League.
He shares the same agent as Gianluca Scamacca, who completed his £30m move to east London earlier in the week.
West Ham are also monitoring developments with Burnley's Maxwel Cornet but are yet to make a move.