This most definitely isn't the case. He's highly rated by the club, he's only recently turned 20 and has just a handful of first team games under his belt, to suggest he's now at some kind of make or break/last chance saloon point in his Spurs career is ridiculously premature.
Its not.
It doesnt matter how highly rated a player is, sooner or later they need to "step up". If they dont, then they move on - its life in football.
Onomah has had two seasons on the fringes (debut 2 and a half years ago iirc), and a lot of opportunities to stake a claim, and, well, hasnt...
Compare to Winks, who is of a similar age, similar position and has had similar (potentially less?) opportunities. Winks is without doubt a player relied upon in the first team/squad. Onomah is not.
Onomah has remained on the fringes, never really pushing on.
With the club and squad as it is, there is only so long that is acceptable. And only so long before another player is pushing for that same position, who is also highly rated, who will get chances...
So much comes down to timing, and taking opportunities as they arise. Let the pass and things just dont work out.
I firmly believe this loan is that make or break situation.
By next summer when he returns we will have strengthened, so he will really need to have proven he deserves a spot in the squad. And if he hasnt, he will have had a season to advertise himself to potential suitors (of which I have no doubt there will be many, especially at a championship level).
As well as for himself, having played a full season of regular games, he will likely want to continue regular football - which will mean he will likely face a decision himself outside of the clubs intentions.
For a young lad out on his first loan, this doesn't strike me as someone passive, quiet and not wanting to get involved. It may be that playing amongst/against more inferior players than he has been accustomed to is giving him more confidence. He seems to be grasping the opportunity, which is great to see. Let's hope he continues to improve and thrive at Villa.
It doesnt, and believe me Im made up about it. I think the summer tournament has done him the world of good, and the loan is an opportunity he understands is something he needs to really grasp. I would love it if he came back stronger and ready to influence the team, it would be amazing - the lad clearly has a lot to work with. IF he can step up and push on he could be something really special. Now is the time to find out.
I also hope he continues to improve. I think the Championship is a strong division and any weakness will be found out - Im hoping this is one of those situations where he leaves as a boy and returns as a man.