Ireland boss Martin O'Neill has been largely unable to rely on the pair for his side's key Euro 2016 qualifiers.
Neither featured in last month's fixtures with Gibraltar and Germany, however, both played in Everton's subsequent 3-0 Premier League win over Aston Villa after that international break.
Midfielder McCarthy also sat out last Friday's 1-0 loss to Scotland with a hamstring complaint, defeat leaves Ireland fourth in Group D.
And assistant coach Keane has now proportioned blame with Everton manager Roberto Martinez for Coleman and McCarthy's patchy international service.
"I worry that he [McCarthy] is under lots of pressure, particularly from Everton's point of view," Keane said.
"Every time an international match comes around, it always seems to be Seamus and James who are under pressure. They're turning up or they mightn't turn up, or they're struggling.
"I think Martin has been more than fair when it comes to friendlies. These are big qualifying matches now.
"Ask most international managers and it's a difficult role when a player turns up and he isn't quite fit or he is struggling, we've had that a number of times with lots of players.
"It's the big downside of international football, you have to be fair to their club and the player, but you also want them out there representing your country. It's difficult for James as well. There is a player between the two managers, I know from experience, they're under pressure.
"You always get the impression from Everton that Seamus and James are both barely able to walk, that type of thing. So when they turn up and they're walking through reception, it's 'Praise the Lord'.
"If it carries on next year, it's going to put a lot of pressure on James. Roberto has never played at senior international level and maybe he doesn't realise how big the games are for us.
"We could argue all day, I just think we need to get the balance right for the qualifiers. I think Martin has been more than good."
