Lafferty signed for Norwegian side Sarpsborg 08 this week but has not trained since being released by Rangers five weeks ago.
Lavery has starred in Linfield’s run to the Europa League play-off stage.
Uncapped Ross County defender Callum Morris is included and Motherwell midfielder Liam Donnelly is called up.
Donnelly, 23, has been in prolific form in a new midfield role for the Scottish Premiership club, scoring seven goals in seven matches.
The record appearance holder for his country’s Under-21s and a former captain of that side, his only senior cap to date came as a substitute in a friendly against Chile in June 2014.
Michael O’Neill’s side play Luxembourg in a friendly at Windsor Park on Thursday 5 September and then host Germany in a Euro 2020 qualifier three days later.
Morris, 29, has been included in previous Northern Ireland squads since switching his allegiance from the Republic of Ireland, for whom he played at U21 and U19 level.
Defender Gareth McAuley is left out as he is currently without a club, while Daniel Ballard is injured and Conor Hazard and Mark Sykes are both omitted.
Lavery has scored four goals for Linfield since joining the Irish Premiership champions from Everton in the summer.
The 20-year-old was on target with a long-range effort in the Europa League qualifier against FK Sutjeska and found the net twice in the first leg of the play-off tie with Qarabag, including a stunning individual goal.
Lavery, whose only previous senior international appearance was in a friendly against Costa Rica in June 2018, will be part of the NI U21 squad and O’Neill indicated at the squad announcement on Wednesday that he can be drafted in “if needs be”.
Lafferty was released by Rangers in July after the final year of his contract in his second stint with the club was cancelled by mutual consent.
The striker has amassed 20 goals in 73 appearances but has not scored since a 4-0 victory over Azerbaijan at Windsor Park in November 2016.
Northern Ireland are top of Euro 2020 Group C, having won the first four matches of a qualifying campaign for the first time.
Home wins over Estonia and Belarus in Belfast in March were followed by victories away against the same opposition in June.
Germany are three points behind Northern Ireland but with a match in hand – at home to the Netherlands on 6 September.
Northern Ireland: Goalkeepers: McGovern (Norwich City), Peacock-Farrell (Burnley), Carson (Motherwell); Defenders: J Evans (Leicester City), Cathcart (Watford), McLaughlin (Sunderland), LeWIS (Norwich City), Smith (Hearts), Flanagan (Sunderland), Morris (Ross County); Midfielders: Davis (Rangers), McGinn (Aberdeen), C Evans (Blackburn Rovers), Dallas (Leeds Utd), Ferguson (Millwall), McNair (Sunderland), Saville (Middlesbrough), Jones (Rangers), Whyte (Cardiff City), Thompson (Blackpool), Donnelly (Motherwell); Strikers: Magennis (Hull City), Washington (Hearts), Boyce (Burton Albion), Smyth (Wycombe Wanderers).