Clingan captained an under-strength side in O'Neill's second game in charge - a 6-0 demolition in Holland - but has been missing from recent squads after an unsettled season at club level.
Having decided to leave Coventry at the end of the last campaign he spent the first part of the season without a club and then had an unsatisfactory spell with Doncaster.
He is now back in action with Kilmarnock and turning in some impressive performances.
"Sammy has had a difficult six or seven months and the club situation has been a bit up and down," O'Neill said.
"I encouraged him in coming to Scotland, that it would be a good option to consider and I've seen him three times now. I've been impressed and he's getting better and better.
"It's great to have Sammy back in the squad because he's an important player for us."
Windsor Park favourite McCann is also back involved having been on the periphery during the first four qualifiers.
He is currently helping Peterborough battling relegation from the npower Championship - an experience O'Neill believes can be beneficial to the national side.
"It's good to have Grant back," he said. "He's played a lot of football recently and his club are in there fighting for survival in the Championship.
"That means he's playing a lot of high-pressure games and that bodes well for him coming in with the nature of the matches we have in the next week or so."
Meanwhile, O'Neill will allow suspended duo Kyle Lafferty and Chris Baird time away from the squad for the first part of the double header.
The pair will both miss Friday's visit of Russia but have been named in a 26-man group with a view to featuring against Israel four days later.
And while they will be in Belfast for the next few days, O'Neill does not intend to include them in full training until the first fixture is done and dusted.
A little free time back home may come in particularly handy for Lafferty, the former Rangers striker who now plies his trade in Switzerland with Sion.
"With both players there is no real benefit to having them (training) with us now, so we'll look to bring them in later in the week when the focus turns to the Israel game," said O'Neill.
"That gives the likes of Bairdy and Kyle the chance to see family back here in Belfast. They're at the stage of the season where two days off and away from it won't harm them in any way or affect them fitness-wise at all.
"It's always difficult to be involved when you know you can't play. it's not great for them and it's not ideal for the team either."