...he has a high chance to play all 48 minutes (or more in case of OTs)
will this cause his game shape to be sloppy/poor?
1)Not this week - GS will stay at respectable.
2)All games (division, cup, SC, not PL or BBB) counts. The sum of minutes played in those games in the week* will matter. The vast consensus is that 50-80 minutes per week is ok, ideally around 60. However, minutes balance from previous weeks (in the same season only I guess) is considered too, so it is hard to tell what the result will be. It looks to be more harsh and harder to keep a level of game shape above respectable than on lower levels of game shape.
Hints:
- Check Weekly Stats for summary of minutes played of your players.
- Notice doctor with specialty Massage should help to deal with extensive minutes - so more than 80 is more acceptable.
- Change in game shape is not marked by green arrow as change in skills are.
- Training of game shape is almost always waste of training.
- Injured players don't play and slowly losing their level of game shape. However is easier to get it back for example from mediocre to respectable than go from respectable to proficient. At least I think so.
*(from Friday to Friday - training update matters here - check weekly schedules in rules for more info if needed)
So no, it won't cause poor game shape.