The 33-year-old returned to the Premier League after two seasons at Bayer Leverkusen, helping them win their first-ever Bundesliga title in 2023-24.
Xhaka has since been integral to everything good that is happening at Sunderland with the newly promoted side sitting in fourth.
Speaking on BBC's The Wayne Rooney Show, the former Man United forward was full of praise for the midfielder, saying: "Coming back to the Premier League, you wonder if he can do it.
“Obviously, with a promoted team as well coming up, what impact could he have? But he's probably been the signing of the season. He has been brilliant.
"When he had the situation with Arsenal, when he fell out with the fans, it showed his character to go and play for Arsenal again.
“To get through that and then go and perform for Arsenal, and then at Leverkusen to be part of a team to beat Bayern Munich to the title for the first time in over 10 years has shown what a good player he is."
Rooney went on to praise Xhaka’s impact off the pitch too, adding: "Sunderland have got a very young squad as well. He'd almost be like a father figure and he'll be a big help for the coach as well to be the in-between man as captain.
“And they made a lot of signings in the summer, he'll be a massive help for the manager and with those players, for sure, using his experience."