The 29-year-old will make his debut in a top-class World Rally Car in Wales, even though he hasn't yet won the WRC 2 category - which had originally been a stipulation in order for Kubica to cement a works WRC drive on one event this season.
The Pole can win WRC 2 by finishing in second place on next week's Catalunya Rally.
Talking about Kubica's step up for this season's WRC finale, Matton said: "It's true that, as things stand, he hasn't won the [WRC 2] title.
"But, even if he doesn't win it in Spain, he has still had a very successful season. He is, therefore, perfectly entitled to have a go at Wales Rally GB.
"There is no doubt that his motivation and professional attitude mean he can set his sights on securing a good result."
Kubica said he was looking forward to gaining experience from his Rally GB debut.
"Wales Rally GB wasn't part of my original programme," he said.
"So I'm very happy to be able to have this precious experience.
"This one-off outing for the works team is a great opportunity for me, but also a huge challenge."