Jones has a toe problem while Charteris has a wrist injury and both are major concerns ahead of Wales' Six Nations' opener against Ireland in Dublin on February 5, meaning extra emphasis is placed on Opsreys' Ian Evans.
"It's good to have Ian back," said Gatland. "It's been a shame as over the last couple of seasons as he has been unfortunate with a lot of injuries and it is good to see him back in there as there is the potential that Alun Wyn Jones and Luke Charteris could both be out for the Six Nations.
"So it's nice to have someone of that quality and ability back in the squad.
"We are sending Luke to the surgeon and he potentially needs an operation on his wrist, similar to the one Jamie Roberts had a little while ago, so he could be out for four or five months."