McCarthy has developed through the youth team with Targett, and he has been impressed by the left-back's rapid progression.
Targett has started to break into the Saints' senior squad, and he has made 10 appearances for the Saints so far this campaign.
And McCarthy, who recently joined Wycombe Wanderers on loan, said of his teammate: “I still keep in touch with all the lads who came through at Southampton, like Luke Shaw and Calum Chambers, but my best friend there is Matt Targett, who is doing really well in the first team at the moment.
“I have played with Matty since the U8s and we've always been in the same age group, so to see him doing well, I would say he inspires me most. He's not been out on loan, but centre backs sometimes take a different path.”
McCarthy has not been exposed to senior football as much as Targett during his career to date, and his loan spell at Wycombe should be good for his development.
The 19-year-old has made just one appearance for Southampton so far, and he will be keen to show what he can do with the Chairboys.
By joining Gareth Ainsworth's side he has joined a League Two promotion fight, and there will be pressure on him to show his class, if he wants to stay in the team.
If McCarthy can impress, then he will know that Southampton are a side renowned for handing their most promising youngsters chances, giving him reason to be optimistic for the future.