Australian-born Ball qualifies for Wales thanks to his father, who is from Colwyn Bay.
"Sam is one of the best at stealing and pinching ball at the breakdown," said Gatland. "We are lucky to have two excellent sevens but Sam gives us some physicality."
Davies is likely to be given another run-out for the Scarlets against Treviso this weekend, having played just 40 minutes in the past two and a half months.
"Jonathan isn't quite right, he is training with us and will have another game next week," added Gatland.
WALES (v Ireland)
: Leigh Halfpenny (Cardiff Blues), Alex Cuthbert (Cardiff Blues), Scott Williams (Scarlets), Jamie Roberts (Racing Metro), George North (Northampton Saints), Rhys Priestland (Scarlets), Mike Phillips (Racing Metro), Gethin Jenkins (Cardiff Blues), Richard Hibbard (Ospreys), Adam Jones (Ospreys), Andrew Coombs (Newport Gwent Dragons), Alun Wyn Jones (Ospreys), Dan Lydiate (Racing Metro), Sam Warburton (capt - Cardiff Blues), Taulupe Faletau (Newport Gwent Dragons).
Ken Owens (Scarlets), Paul James (Bath Rugby), Rhodri Jones (Scarlets), Jake Ball (Scarlets), Justin Tipuric (Ospreys), Rhys Webb (Ospreys), James Hook (Perpignan), Liam Williams (Scarlets).
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