United travel to the south coast looking to maintain momentum, after beating Liverpool at Old Trafford on Monday night, as Casemiro watched on.
The Brazilian enforcer could make his Reds bow against the Saints after training with his new team-mates for the first time at Carrington on Thursday.
Ahead of Saturday's lunchtime kick-off, Casemiro shared his eagerness to play for United in the "great league that is the Premier League", and looks to be thrilled at the prospect of pulling on the shirt for the first time.
“I'm looking like a 20-year-old boy, wanting so badly to play for Manchester,” the 30-year-old told ESPN Brazil.