Bit of a weird career at Celtic Griffiths has had so far. Came in and none of the fans really wanted him, but started banging in the goals and everyone was quiet. Under Deila he featured very early on in the season but was used as a winger and wasn't very good. Since then two strikers have been signed (Guidetti and Scepovic) and he's been pretty much warming the bench domestically and on the European stage.
But as you mentioned Guidetti hasn't been that good lately and Griffiths has been decent when called upon. Think he might get a start in the next game so he's just got to take his chance really. The only problem is is that Scepovic has also looked quite useful but Deila likes to play with only 1 striker. Gonna be hard to keep them all happy.
Anthony Stokes has been great for Celtic so far this season btw, he's been playing as a left winger. Worked really hard to remain in the managers plans, lost tonnes of weight and has really bought into what Deila is trying to achieve.