Alen Halilovic is coming into form for loan side Sporting Gijon.
The central midfielder, 19, was signed by Barcelona in 2014, but found first team opportunities hard to come by for last season's Champions League winners.
He had to settle for playing for Barcelona's B side, and this season sought a loan move.
The Guardian reported in June that West Ham were exploring the possibility of signing Halilovic on a season long deal, with new manager Slaven Bilic very much aware of his countryman's talents.
Halilovic netted his first La Liga goal at the weekend, scoring in a 2-1 win over Espanyol.
He has two assists already this season, and is beginning to flourish with regular game time, playing as an attacking central midfielder.
Combined or alternated with Manuel Lanzini, Halilovic could have been a shrewd addition to West Ham's squad, and helped them unlock stubborn defences at key moments in games.
With a bright future at Barcelona surely ahead of him, the Hammers may have missed their one and only chance to bring in the superstar-in-waiting.