So again, in the hope that you may actually answer this time, how does that player alter our level of creativity?
In order to do so, they will need to be on the ball. Last time I checked, in order to be allowed to do that, they would either need to start or come on as a sub. Which leads us neatly back to my question regarding this player and how it would affect Eriksen's time on the ball.
If he's fit enough to run further than pretty much anyone else on the pitch, then he's fit enough to play.
Competition for Eriksen would be great. The problem is, that competition would need to be good enough to Eriksen to fear he might lose his place to that player for the kind of motivation you are suggesting. Eriksen is one of the best in the world in his position, Barkley is barely the best at Everton. If you genuinely think we can get someone at or near Eriksen's level to come and get splinters in their arse at Spurs, I'd love to hear who.
As always, it's nice to have some facts to back up opinions.
Eriksen's history in the PL:
CLICKY
He's actually scoring at a better rate this season than ever before in the PL (small sample size).
EDIT: That link also shows that he's played 36, 35 and 38 PL matches in the last three seasons. That doesn't suggest a player who struggles with fitness/stamina to me.