After Naruto's victory against Kakazu, Kakashi internally addresses Sasuke, noting how Sasuke is the inspiration always pushing Naruto forward to become strong.

Kakashi musingly directs to Sasuke the question of "it's you who makes him strong...you know that, don't you Sasuke?"

Of course, Sasuke is not at all aware of how hard Naruto is pushing himself on Sasuke's behalf, and there is no way Sasuke could know. Based on the timing of Kakashi finally acknowledging Sasuke's existence in Shippuden on a more personal level, it seems Kakashi's mention of Sasuke is more a matter of Kakashi wanting Sasuke to acknowledge how hard his new favorite student Naruto is working and pushing himself rather than any actual interest in how Sasuke feels. Hidden in Kakashi's line seems to be an underlying annoyance or sadness that Sasuke isn't around to appreciate all Naruto's hard work, or perhaps it's merely sadness that Naruto is trying so hard to catch up to Sasuke yet Sasuke isn't even there to witness it.

Personally, to me this line comes across as Kakashi wants to show off his new trophy student, and is a bit sour that the desired audience isn't there to see it. Naruto has been working hard for years but Kakashi only abruptly cares about Naruto's progress when Naruto is actually shaping up to be prodigiously good (whereas I guess all of Naruto's efforts before didn't evoke enough emotion in Kakashi for him to feel anything or desire to see Naruto to achieve his dream of getting Sasuke back). At least, Kakashi's line seems more interested in Naruto's feelings and wants, not Sasuke's.

Though however one interprets this scene, Kakashi internally speaking to Sasuke does indicate that Kakashi wishes Sasuke were there to witness this moment of Naruto's triumph.