He was ok in his first 60 minutes in PL and needs time to adapt obviously. The lack of support for him from midfield and the wings was clear as day and you have to give him the benefit of the doubt. The midfield line was so deep so he was isolated up front at times but had a good link up play with Rooney and Sigurdsson. And Cenk's English looks quite good so that's a bonus in communication with his teammates too.
The likes of Real Madrid and Borussia Dortmund also lost at Wembley against Tottenham this season(both 3-1 i think) so it's not a great shame to lose to them away but Big Sam needs to adress his midfield's deficiencies to get a good balance tactically and support his forward line so we can get a clearer picture of Cenk's ability to make his contribution. A winger or two in this window would also help as Siggy is more of a no 10 and Bolasie is useless.
The blindfold defending from Turkish fans is appalling though

Cenk is a player who never played at the top level before and only time will tell if he is good enough or not.Big Sam knows that and that's why he said this transfer is not a guaranteed success but a gamble.Let's hope he will be a big hit as he looks a decent guy.