The Hammers have lost Felipe Anderson to injury while Michail Antonio has been struggling with hamstring injuries all season.
Meanwhile, Diangana has shone under former Hammers boss Slaven Bilic in the Championship this season, bagging five goals and six assists so far. However, the 21-year-old suffered a hamstring injury against Stoke on Monday night having only just returned from a back injury.
His return to the club this month had been discussed at length since Moyes's arrival, only for his latest injury to put an end to those plans.
"Having Grady back would have given us a bit of speed, something different," said Moyes. "But in the same breath he’s playing for a team which could get promoted and the experience he will get from that, hopefully he will learn from.
"Playing in a winning team will be good for him. If we had everybody fully fit it would have been much harder for him. But the more important thing for him is the prospect we’ve got. He had a hamstring and our worry is that it’s a recurrence."
Moyes is keeping a keen eye on Diangana for next season, however. The Scotsman is keen to foster a younger, fresher squad for the start of the season, with Josh Cullen - currently on loan with Charlton - another he is impressed by.
"100 per cent, all the young players," said the West Ham boss. "I’d like to have a really new, young team. Having them around would be good. We think Grady has got something as well."