The 24-year-old forward sealed a £30 million switch to Anfield from Southampton on Tuesday, signing a five-year deal with the Merseyside outfit according to The Guardian.
The duo have been Senegal team-mates since 2012 and Kouyate sent his compatriot a good luck message, along with an Instagram snap of Mane at his unveiling.
Congratulations my bro.all the best for your new team.— cheikhou kouyate 8 (@PapiCheikhou) June 28, 2016
YALLA nala djik amine… https://t.co/4DFCocBjns
Kouyate had earlier retweeted Liverpool's confirmation of Mane's arrival.
It is nice to see the Hammers star be so supportive of his friend given that both may well be rivals next season.
This time last year, the notion of West Ham being a rival to Liverpool was perhaps fanciful, but fast forward 12 months and the Irons - who finished above Jurgen Klopp's side last term - have improved hugely under Slaven Bilic.
Still, both sides might well go into the season with different ambitions. For West Ham, Bilic and co would settle for a Champions League spot, whereas this £30 milllion acquisition suggests that the Merseyside could be aiming for the title.
It will be Klopp's first season, but fans of a club like Liverpool will always be aiming for the Premier League.