Strikers Will Grigg and Conor Washington return to the Northern Ireland squad for the opening Euro 2020 qualifiers against Estonia and Belarus.
Sunderland's Grigg has missed Northern Ireland's last three games because of injury with Washington unavailable for personal reasons since last September.
Uncapped Arsenal youngster Daniel Ballard, 19, is given a first call-up.
Washington's Sheffield United team-mate Oliver Norwood will miss the opening qualifiers for personal reasons.
Estonia travel to Belfast for the first Group C match on Thursday, 21 March and Belarus also visit the National Stadium at Windsor Park three days later.
Goalkeeper Trevor Carson and full-back Michael Smith are unavailable because of injury.
O'Neill says Ballard has had 'rapid rise'
Defender Ballard, who is a regular in Arsenal's under-23 team, has earned four under-21 caps.
One of his under-21 appearances saw Ballard score a late winner in a qualifier against Iceland last October.
With centre-backs Gareth McAuley and Aaron Hughes both now 39, O'Neill has opted to bring Ballard into the squad.
"Daniel Ballard has had a rapid rise with us. He was in the under-19s last year and did very well and we promoted him to the under-21s for the last few games of their campaign and he's been playing regularly at Arsenal at under-23 level," added the manager.
"We are bringing him in for the experience as well but it's an indication of where we are at the moment as both Gareth McAuley and Aaron Hughes aren't going to go on forever and neither are playing regularly at their clubs as well.
"So I thought it was important to bring Daniel in because within the next 12-18 months he has the potential to be a regular in the squad."
O'Neill 'concern' over squad's lack of recent action
Motherwell keeper Carson's absence as he continues to recover from deep vein thrombosis means Leeds' Bailey Peacock-Farrell, Norwich's Michael McGovern and Conor Hazard will battle for the goalkeeper's jersey.
However, none of O'Neill's three keepers are currently regulars with their clubs which the manager admitted on Tuesday "is not the ideal scenario".
"It's a situation that is out of my control," added the Northern Ireland boss.
"We've had this scenario before. Michael [McGovern] played virtually most of the campaign for Russia when he wasn't starting at Norwich and he played and never let us down.
"Whoever goes in, whether they're first choice for their club or not, they'll have to deal with being first-choice for us."
And the keepers are far from being the only players who are not getting much first-team action with their clubs.
"I think there's 15 or 16 players in that 27 that didn't start for their clubs at the weekend so that's always a concern," added O'Neill.
"We just have to hope that when they come in that they've got enough in their legs to be able to take care of the two games as well."
Northern Ireland squad
Goalkeepers: McGovern (Norwich City), Peacock-Farrell (Leeds United), Hazard (Partick Thistle - loan from Celtic)
Defenders: Hughes (Hearts), McAuley (Rangers), J Evans (Leicester City), Cathcart (Watford), C McLaughlin (Millwall), McNair (Middlesbrough), Lewis (Norwich City), Flanagan (Sunderland), Ballard (Arsenal)
Midfielders: Davis (Rangers - on loan from Southampton), McGinn (Aberdeen), C Evans (Blackburn Rovers), Ferguson (Millwall), Dallas (Leeds United), Saville (Middlesbrough, loan), Jones (Kilmarnock), Whyte (Oxford United), Thompson (Blackpool)
Forwards: Lafferty (Rangers), Magennis (Bolton Wanderers), Boyce (Burton Albion), Smyth (Accrington Stanley - on loan from QPR), Grigg (Sunderland), Washington (Sheffield United)