Swansea University student Liam Stacey, 21, from Pontypridd, admitted inciting racial hatred over remarks about the Bolton Wanderers player, who collapsed during a FA Cup tie at Tottenham.
A district judge in Swansea called the comments "vile and abhorrent".
Muamba, 23, who suffered a cardiac arrest, is still in intensive care.
Sentencing Stacey at Swansea Magistrates' Court, District Judge John Charles told him: "In my view, there is no alternative to an immediate prison sentence.
"It was not the football world who was praying for [Muamba].... everybody was praying for his life."
Stacey broke down in tears as he was led away to begin his jail term.
