World Cup - Ireland call up Sherry, Wales trio fit
Best injured his shoulder in a tackle in the 36-6 victory over Italy in Dunedin on Sunday which ensured Ireland topped Pool C.
"The medical team has worked hard with Rory over the last 24 hours and he's reacted well to it and we're very pleased with the response. He's not totally ruled out," said assistant coach Mark Tainton.
"His chances at the moment, they're long. He's doubtful for this weekend but he's not ruled out of the competition."
Ireland manager Paul McNaughton said they expected Sherry to arrive in New Zealand on Thursday.
Sherry is the second hooker called into the Ireland squad since the tournament began with Shane Varley coming in after Jerry Flannery tore his left calf muscle at training before their match against Tri-Nations champions Australia.
Sean Cronin is likely to step into the starting role for their clash with the Welsh if Best is, as expected, ruled out of contention.
"I've been in this situation before," Cronin said.
"In the autumn internationals just gone by Rory picked up a bad injury against the All Blacks, so I had to come on early in that game and prepare for the following week against Argentina.
"Obviously it's a different level here at the World Cup but I've done it before."
Meanwhile, Wales have received a major boost ahead of the quarter-final with three key players passed fit to resume full training.
Full-back James Hook, wing Shane Williams and flanker Dan Lydiate are all expected to be available for Saturday's showdown in Wellington.
Hook (shoulder) and Lydiate (ankle) both went off during Wales' punishing Pool D victory over Samoa in Hamilton 16 days ago and have not played since, while Williams missed runaway victories over Namibia and Fiji due to a thigh strain.
But they will take part in training on Wednesday, giving Wales coach Warren Gatland a full squad of 30 from which to select his starting line-up.
Lydiate's recovery has proved particularly impressive after he departed with ankle ligament damage just 10 minutes into the Samoa game.
As part of his initial bid to regain fitness, he woke at two-hourly intervals throughout the night to ice his ankle, and that approach now looks as though it has paid off.
Former Wales captain Ryan Jones took over from him in the Namibia and Fiji fixtures, while Leigh Halfpenny and then Lee Byrne deputised for Hook, with Halfpenny moving from full-back to wing against Namibia and Fiji.
"Dan, James and Shane have all been passed fit to train tomorrow," said Prav Mathema, the Welsh Rugby Union's national medical performance manager.
"Pending any adverse reaction, we expect them all to be available for selection against Ireland this weekend.
"Gethin Jenkins and Sam Warburton are also both fit for selection following calf cramp experienced during the end of the Fiji fixture."