Wales' interim head coach has made a major call by leaving Lions Test scrum-half Mike Phillips on the bench for Saturday's November series opener against Argentina.
Bayonne No 9 Phillips is among five members of the Wales squad plying their trade in French or English club rugby.
Club commitments meant none of them were involved during last week's punishing training camp in Poland, which was viewed by Howley as critical towards the autumn preparations.
Wales' home-based players travelled to Spala because terms of a participation agreement signed between the four professional regional teams and Welsh Rugby Union ensured their availability.
But the exodus of players could continue, with Cardiff Blues centre Jamie Roberts and Newport Gwent Dragons flanker Dan Lydiate among those being linked to big-money moves overseas.
"It is a very tough choice I have got to make, and one I haven't made yet," said Roberts, who has been recalled after injury to face the Pumas.
Contepomi returns for Pumas' Cardiff clash
Argentina have recalled Felipe Contepomi to face Wales at the Millennium Stadium on Saturday.
The 35-year-old former Leinster back, currently at Stade Francais, sat out the Rugby Championship due to an agreement between the Argentinian Rugby Union and the French clubs and was not named in coach Santiago Phelan's initial squad for this tour.
But with Biarritz centre Marcelo Bosch unavailable due to his own club commitments this weekend, Contepomi comes back into Phelan's starting XV to win his 79th cap as part of a side showing six changes and two positional switches from the defeat to Australia.
Alongside Contepomi in midfield will be former Harlequins and Stade Francais three-quarter Gonzalo Tiesi, who will make his first appearance since the 2011 World Cup.
Star out-half Juan Martin Hernandez has been shifted to full-back, the position where he made his name, with Bordeaux-Begles' Nicolas Sanchez preferred in the No 10 role.
England ready to blood newcomers
Launchbury, who initially only linked up with the squad on Monday as injury cover for Tom Palmer, has been preferred to Saracens lock Mouritz Botha and Harlequins' George Robson.
England coach Stuart Lancaster will confirm his starting XV tomorrow.