Koeman left midfielder Mane out of the Saints’ starting lineup for the Premier League game against Norwich City on Saturday.
According to BBC Sport, the Dutchman made the decision because the Senegal international missed a pre-match meeting.
Mane started the match at Carrow Road on Saturday on the substitutes’ bench and came on in the 80th minute.
Southampton lost the encounter 1-0 and now find themselves 13th in the league table, seven points above the relegation zone.
Dixon has backed Koeman in his decision over Mane and has written on Breathesport.com: “Rules are rules. I applaud RK.
“George Graham too had a strict code of conduct when it came to time keeping. He taught me that the correct arrival time for a 10.00 meeting wasn't 10.00. It was 9.55!”
Mane is one of Southampton’s best players, and he was missed against relegation candidates Norwich.
The 23-year-old has scored three goals and created 27 chances in 20 Premier League appearances so far this season.
Southampton are 13th in the Premier League table at the moment with 24 points from 20 matches, seven points above the relegation zone.