Playtime on player progress

I wondered if anyone knows whether one requires to let a player play as many matches as possible to assure a maximum progress speed, or if one just has to keep the player 'match fit' in order for the player to progress optimally.

As I am doing some network game where I play Real Madrid C.F. and someone else plays F.C. Barcelona and I just bought Miralem Pjanic and Javier Pastore in addition to the attacking midfielders I already possess. Recently, Kaká has come back from his long-term injury causing a bit of an 'overkill' on the attacking midfield. Therefore, I wondered if it would be better to send Pjanic out on a loan (where his progress is likely to suffer from inadequate training levels) or if I should keep him at Real Madrid and rotate him frequently with Pastore and/or Kaká (also allowing for a significantly higher level of training and customised training schedules).

I've once read that an average of about 25 minutes a game does the trick. Along with great training ground and coaching staff. But the main factor in a players growth is playing time.
Personaly I only send them on loan if they stand still in their progress meanig the 25 min average doesn't do the trick anymore. Also tutoring a player gives the player a boost in their ability.

Be very careful where you send your players on loan I play as arsenal and some of my players came back from being on loan unhappy and with a worse potential ability than when they left

But if you leave them in the reserves they may progress slightly over a few years

Patients is the key here

I prefer to keep my youngsters in the reserves than send them out at loan, then I know their on good training schedules with good coaches and they're staying match fit from playing reserve games. I see more progression from this than sending them out on loan.

Do the coaches stats gradually decline over time as with previous games? This was something i could never understand