Sammy Lee and Dave Watson have been appointed to Southampton's coaching staff.
Koeman took charge of Southampton last month and will be joined in the dugout by Lee, who serves as first-team assistant coach, while Watson joins as senior goalkeeping coach.
Executive director Les Reed told the club's website: "I am extremely happy that we have been able to appoint three highly-respected and talented coaches to these important positions in our coaching structure.
"Sammy has a wealth of experience from his time with Liverpool and Bolton, as well as from his long association with the England team.
"He will work closely with Ronald, Erwin and Jan, and will play a big part in the day-to-day coaching of the first team.
"Despite his relatively young age, Dave has already built up an impressive CV and is regarded as one of the most talented goalkeeping coaches in Europe, and has only just returned from the 2014 FIFA World Cup finals.
"That we have been able to attract Sammy and Dave to Southampton is testament to our ambition to continue growing as a club, and shows our commitment to develop talented footballers at all age levels."
