Yes, we can't say for sure but Mata's prolonged absence from the team reminds me of the time this season when Luiz couldn't get any game time after his defensive blunder in one match (can't remember against which team). But eventually Luiz did find his way back into Mourinho's plans, so I believe Mata will, although it could be longer (depending on squad fitness). The flip-side is you have to remember players like Andre Schurrle have also not featured as much. In fact, Jose whenever possible, likes to keep the same back four and the same attacking midfielders. The only real changes happen in CM (depending on fitness/who's available) and ST (depending on the opposition, Torres for space and Eto'o against tight defences).