Southampton’s Jack Stephens has also joined up with Aidy Boothroyd’s Three Lions ahead of the Euro qualifiers against Kazakhstan [Thursday 6 October] and Bosnia & Herzegovina [Tuesday 11 October].
Meanwhile, both Dominic Iorfa and Matt Targett have not met up with the U21s and instead will remain with Wolverhampton Wanderers and Southampton respectively for further assessment on injuries.
Whilst they are definitely ruled out of the away trip to Kazakhstan, they remain under consideration for the Bosnia game depending on how they respond to treatment at their clubs.
Meanwhile, Sheffield United midfielder Louis Reed has been called into the U20s squad to replace Onomah, as they prepare to face Netherlands, Germany and USA in a mini tournament on home soil over the next week.
Tickets for the U21s' game with Bosnia & Herzegovina at Walsall's Banks's Stadium on Tuesday 11 October cost just £1. Find out more details by clicking here.
And the U20s take on the Dutch in Oldham on Wednesday, Germany in Huddersfield on Friday and USA at Rochdale on Monday 10 October. Tickets for those games cost just £3 for adults and £1.50. Click here for more details on those games.