Wales have just two fixtures left - at home against England on Saturday and Argentina the following week - before coach Warren Gatland names his 30-man World Cup squad.
Hooker Rees, Wales skipper last season, is currently battling to overcome a neck problem, while prop Jenkins has had toe and calf trouble and last played eight months ago.
But such is their value to Wales' World Cup campaign, which kicks off against reigning champions South Africa in Wellington, that they could board the plane to New Zealand on August 31 without playing this month.
"You can't underestimate how important playing is," said Wales forwards coach Robin McBryde.
"You can do as much training as possible, but you cannot match the intensity of international rugby."
But regarding the World Cup, McBryde added: "We would take Gethin and Matthew if they had not played any rugby.
"There are certain players who warrant a certain amount of special attention, and those two individuals fall into that category, looking at how important they have been to us in the past.
"There are no major concerns about Gethin Jenkins. We would have liked to have seen him play last weekend, but he was not quite right.
"We are not going to rush or risk anyone at this stage. He has undergone quite a bit of rehabilitation and progressed really well.
"He has worked hard, and we did not want to undo all that good work."
Gatland will name his team tomorrow for the England rematch, and while changes are expected, there might not be wholesale switches given an encouraging Wales display at Twickenham last weekend.
Wales were denied 23-19, but they outscored their hosts 3-2 on tries and looked the fitter team during a dominant display in the closing quarter.
McBryde added: "Generally, I thought we finished the game particularly strongly and put England under a bit of pressure.
"We have some nice selection headaches at the moment."
There could be starts for centre Gavin Henson this weekend - it would be only his second Test appearance in more than two years - hooker Lloyd Burns, prop Adam Jones, lock Luke Charteris and back-row forward Ryan Jones, yet Gatland is unlikely to tinker too much.
It would be a rare recent start for 6ft 9in Newport Gwent Dragons lock Charteris after playing a support role to an established second-row pairing of Bradley Davies and Alun-Wyn Jones.
Davies and Jones have started 11 of Wales' last 13 Tests, so if Charteris does get the nod from Gatland this weekend then he knows what is at stake.
"They (Davies and Jones) have both cemented their places in the side," said Charteris.
"They've played well over a year and a bit, so it's my job now to push myself and try to get a starting spot in the team.
"That's where the goal is, not just to make the squad, but to land a starting jersey. I have to focus on my own game.
"You want those two playing as well as they can and as well as they are because it's better for the team. I just have to make sure I play a bit better.
"Every time I get an opportunity, whether it is off the bench or in a starting line-up, I have to give it everything. I've got to try to force my way into the team."
Gatland looks set to take three specialist locks to New Zealand, with Ryan Jones providing additional second-row support, although Charteris added: "We've had no feedback on whether they are taking three or four.
"I think everyone is sweating on selection at the moment. The boys have trained hard all summer and a lot of them have raised their standards.
"We are all desperate to make that final squad."
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