There are plenty of players who are always fit and ready to play. Guys like Sanchez, Suarez and Lewandowski just a few examples. I'm pretty sure both Messi and Ronaldo have been injured more than these three for example. When it comes to recovery it has to be said that Messi actually runs very little in the Barca games which surely helps when recovering.
Take a look last seasons CL game against Atletico for example.
Metres covered by player
Atlético
Oblak 4,471
Juanfran 9,911
Godín 9,167
Lucas 8,936
Filipe 9,738
Gabi 11,824
saul 12,160
Koke 12,226
Augusto 11,431 (sub out 90+3 min)
Carrasco 9,855 (sub out 74 min)
Griezmann 11,417 (sub out 90 min)
Savic 0,275 (sub in 90+3 min)
Correa 0,672 (sub in 90 min)
Thomas 2,486 (sub in 74 min)
Barcelona
Ter Stegen 4,603
Alves 7,218 (sub out 64 min)
Piqué 9,802
Mascherano 8,612
Alba 10,995
Busquets 11,013
Rakitic 7,885 (sub out 64 min)
Iniesta 10,252
Neymar 9,134
Messi 7,049
Luis Suárez 9,130
Sergi Roberto 3,674 (sub in 64 min)
Arda 3,204 (sub in 64 min)