Once each country declares its squad that is final, so Rees has to determine whether Thomas can last the two-day event. He commented, "At the moment Martyn has been passed fit by the medics but we want to make absolutely certain. Once you declare your squad you can't change it during the tournament.
"We won't make a decision until as late as possible. If Martyn doesn't make it then Alec Jenkins will come into the squad" stated Rees, whose side goes into the final leg of the World Series buoyed by the success of reaching their first ever Cup semi-final in London last weekend.
"We've had a lot of positive reaction back in Wales" said Rees, adding, "But the problem is that there is an added weight of expectation. Realistically we've set our minimum goal at qualifying for the Cup quarter finals."
Wales are drawn alongside Samoa, France and Italy, all of whom, Rees claims, are beatable. "We play Samoa first and we may catch them cold. Our results against France have been good while Italy are difficult to play against but lack the experience of sevens."
Rees pitted his Welsh squad against Portugal, New Zealand and Kenya in three practice sessions at Myreside in Edinburgh yesterday with all but skipper Jonathan Edwards taking part. Edwards is still suffering from bruising to his shoulder but expects to be fully fit for tomorrow (Saturday).
Pools for Edinburgh Sevens
Pool A : Fiji, Australia, Kenya, Portugal
Pool B : Samoa, France, Wales, Italy
Pool C : South Africa, Scotland, Canada, Russia
Pool D : New Zealand, England, Argentina, Georgia
Jonathan Edwards (Llanelli, Capt)
Lee Beach (Ospreys)
Wayne Evans (Blues)
Dafydd Hewitt (Blues)
Rhodri McAtee (Penzance)
Rob McCusker (Scarlets)
James Merriman (Neath)
Tal Selley (Ospreys)
Aled Thomas (Dragons)
Martyn Thomas (Dragons)
Lee Williams (Scarlets Academy)
Jonathan Vaughton (Ospreys)
Standing by: Alec Jenkins (Llanelli)