The winger was forced off in Saturday’s 1-0 defeat at Liverpool after taking a whack to his heel and is a major doubt for first leg of their last-16 tie in Spain.
West Ham confirmed yesterday that an initial scan revealed no serious damage to his achilles but Bowen is still suffering from significant swelling.
The 25-year-old will undergo further scans this week but sources at West Ham fear it is unlikely he will be fit to face Sevilla.
Being without Bowen for their biggest game of the season would be a major blow to West Ham. The 25-year-old has been their best player since the turn of the year and has scored seven goals in the last 11 games.
David Moyes does remain hopeful that Declan Rice, who missed the defeat at Liverpool through illness, will be able to return on Thursday.
West Ham can take encouragement from the fact that without Rice and, for most of the second half, Bowen they put in one of their best performances in months at Anfield and were unfortunate not to come away with at least a point.
Pablo Fornals, Manuel Lanzini and Michail Antonio, who were all excellent up to the final moment, missed good opportunities to hurt Liverpool on the break.
“The result is the most disappointing thing,” said Aaron Cresswell. “But, if you’re taking positives then the chances we created, on another day we maybe score two or three goals.
“There’s 10 games now in the Premier League and still loads of points to play for. We want to push up that table and finish as high as we can, of course we’ve got Europe midweek and two big games in that.”