He thinks Spurs must be kicking themselves for letting him go and explains:
"Mattie has been fantastic all season and we missed him against Walsall because of the natural width he gives us on the left hand side.
"He was outstanding on Tuesday and has been unlucky not to get so many goals as he deserved.
"There are not many wide players anywhere; you can see the problems England's national team has looking for a left sided player and we are lucky enough to have an English left-sided player in our team playing week in, week out.
"If he keeps going the way he is going people must look at him in the future, without a shadow of a doubt.
"He does give us something different and I am really pleased for him because he is a good lad and works so hard."
Perhaps he has Scottish grandparents and could line up for Christian's national side?
"I wish he did; that would be brilliant!"
Christian feels that Upton Park is continuing to be a good breeding ground for young talent - whether through the ranks or brought in elsewhere, as we have seen with the astute signings Alan Pardew has made, and adds:
"I think one thing that is good about some of our young lads in this league is that you get the chance to find your feet playing week in, week out - and to really establish yourself as a player.
"That is one benefit playing in the first division can have because Mattie has got stronger as the season has gone on playing every week.
"You can learn the game and make your name as a player here and sometimes you can't do that in the Premiership because of the number of foreign players in it."
He feels playing at Upton Park can be especially beneficial for midfielders and strikers and explains:
"We can go and be really attacking in this league and it is great for forward players like Mattie, and I think a lot of young players have gained invaluable experience from playing in this division."
Christian says the team were determined to make amends for Saturday's draw against Walsall and adds:
"We were all disappointed after Saturday when we didn't play at a high enough tempo in the first half.
"But we upped it in the second half and we tried to make Tuesday a continuation of that.
"We scored a couple of goals in the first half and kicked on from there.
"There is a big gap but we have got ourselves to third and it does put the pressure on when teams see West Ham sitting third - it was important to win that game."
As for the trip to the Stadium of Light, he says:
"It will be a tough game and without doubt Sunderland are one of the best teams in this league and that is going to be as hard a game as there is this season."
Christian will be up against former defensive colleague Gary Breen and says:
"It will be nice to see Breeny again, and he will be up for this one; I am told he has been playing well up there.
"Perhaps he didn't really settle at West Ham because we were struggling in the Premiership, and there were a lot of changes in the side.
"He had only signed for a year so there was some pressure on him, as I hope there will be when we play them.
"He is a better player than we saw at West Ham - anyone who wins 60 caps for your country is a decent player."