Bath lock Dominic Day and Exeter prop Tomas Francis have both been included in Wales' 31-man squad for the World Cup announced Monday.

Day was one of the five second rows included in the squad, with Francis, who only made his Test debut last weekend, joining fellow props Paul James, Gethin Jenkins, Samson Lee and Aaron Jarvis.

After the squad was announced by Welsh Rugby Union chairman Gareth Davies at Cardiff's Millennium Stadium, Gatland revealed first-choice lock Alun Wyn Jones had suffered a knee strain during Wales's 16-10 warm-up win away to Ireland in Dublin on Saturday.

Jones is now expected to be sidelined for two weeks, placing a question mark against his availability for Wales' World Cup opener against Uruguay at the Millennium Stadium on September 20.

"We have ended up going for five second-rows, and really because it is such an attritional position, and as a result probably Kristian (Dacey) has been unlucky to miss out at this stage," said Gatland.

"Alun Wyn Jones picked up a little bit of a medial strain on the weekend, which is a couple of weeks, Luke Charteris got a bang on the leg, so we have kind of looked at the squad and said that if players pick up knocks we've got cover for them.

"It's a couple of weeks (for Jones). That engine room is so important for us. I thought he was outstanding on the weekend."

Among the seven players left out from Gatland's original 38-man training squad was New Zealand-born fly-half Gareth Anscombe.

Qualified for Wales through his Welsh mother, Anscombe joined Cardiff Blues from Super Rugby giants Waikato in 2014.

He made his Wales debut in the 35-21 warm-up defeat by Ireland in Cardiff on August 8 but suffered an ankle injury in training last week.

Gatland has included just two fly-halves in Dan Biggar and Rhys Priestland.

"It is incredibly disappointing for those players that miss out," Gatland said.

"It's hard, but you have got to accept that is the nature of professional sport and we are entrusted to make what we believe are the right calls," added the former New Zealand hooker, himself left out of the All Blacks' 1991 World Cup squad.

Wales will again be captained by Cardiff back-row Sam Warburton, who led his country to the semi-finals of the 2011 edition in New Zealand -- a match where he was sent off in an agonising 9-8 loss to France.

The Welsh have been drawn in a tough World Cup pool that features main tournament hosts England and two-time champions Australia, as well as dangerous outsiders Fiji.

As a result, at least one of rugby union's major nations will fail to reach the quarter-finals, with only two teams from each of the four pools qualifying for the last eight.

Gatland's men conclude their warm-up programme at home to Italy, thrashed 48-7 by Scotland last weekend, in Cardiff this coming Saturday.

Wales squad

Backs

Full-backs: Leigh Halfpenny (Toulon/FRA), Liam Williams (Scarlets)

Wings: Hallam Amos (Newport Gwent Dragons), Alex Cuthbert (Cardiff Blues), George North (Northampton/ENG)

Centres: Cory Allen (Cardiff Blues), Jamie Roberts (Harlequins/ENG), Scott Williams (Scarlets)

Fly-Halves: Dan Biggar (Ospreys), Matthew Morgan (Bristol/ENG), Rhys Priestland (Bath/ENG)

Scrum-halves: Gareth Davies (Scarlets), Rhys Webb (Ospreys), Lloyd Williams (Cardiff Blues)

Forwards

Back-row: Taulupe Faletau (Newport Gwent Dragons), James King (Ospreys), Dan Lydiate (Ospreys), Justin Tipuric (Ospreys), Sam Warburton (Cardiff Blues, capt)

Locks: Jake Ball (Scarlets), Luke Charteris (Racing 92/FRA), Dominic Day (Bath), Bradley Davies (Wasps/ENG), Alun Wyn Jones (Ospreys)

Hookers: Scott Baldwin (Ospreys), Ken Owens (Scarlets)

Props: Tomas Francis (Exeter/ENG), Paul James (Ospreys), Aaron Jarvis (Ospreys), Gethin Jenkins (Cardiff Blues), Samson Lee (Scarlets)
Source: AFP