He played two games for Spain, he'll start against City and most likely at Mestalla on Saturday as well. It was good to rest him vs. Deportivo at home when two tough games are ahead of us this week. Can't complain about Lucho's decision this time but Iniesta should started against Celta, especially with Rakitić also not available. I think at least one of Iniesta/Rakitić should start every away game as other midfielders are still too new into the system.
To be honest, I don't particularly like the way Lucho rotates, especially in midfield, because he seems to have divided the playing time between two sides, the starters, who play the best games (Busi - Iniesta - Rakitic), and the other guys, who play what is left (this usually still includes Busi, and then we have Gomes, Arda, Rafinha and Denis). This is the reason why the team is lacking some substance. Because we have the newcomers (I count Arda as a newcomer because of his abnormal first season) who kind of play next to each other, instead of playing next to established Barcelona players that could help them integrate faster.
What I would like is a more mixed approach. I want to see Gomes playing with Busi and Iniesta as well for example, to see how he gets along with two great passers in his close proximity.
It's just me, but I would play Busi - Iniesta - Gomes vs City on Camp Nou, and I would play Rakitic in the away game, where I expect us to dominate less.
I just don't see why we should field Busi - Iniesta - Rakitic in a non-decisive game vs City on Camp Nou. It's the perfect game to play Umtiti and one of the new signings in midfield, because it is a tough game, against a very very good team, and with some pressure, but it is not decisive and City's draw in Scotland works in our favour. These are the games where we have to try 1-2 new players to see how they can play in a working platform against a top rival.
I would field Stegen - Alba, Umtiti, Pique, Roberto - Iniesta, Busquets, Gomes - Neymar, Suarez, Messi.