Complex sentence: Griffiths signed a four-year deal with Scottish champions Celtic for an undisclosed fee on 31 January 2014 and made his debut for Celtic as a substitute in the 2--1 loss in the 2013--14 Scottish Cup fifth round against Aberdeen.
Split into simpler sentences: Griffiths signed a four-year deal with Scottish champions Celtic for an undisclosed fee on 31 January 2014. Griffiths made his debut for Celtic as a substitute in the 2--1 loss in the 2013--14 Scottish Cup fifth round against Aberdeen.