Wagner, a Bayern youth product, officially swapped Hoffenheim for his hometown club at the start of the January transfer window on a two-and-a-half-year deal.
"Whenever I came up against Sandro, I always knew: 'man, it's going to be uncomfortable today'," Martinez admitted in an interview with SPORT BILD. "He reminds me of Mario Mandzukic."
Two physical centre-forwards standing at over six-foot tall, it is a fair comparison to make.
Mandzukic, brought in around the same time as Martinez in summer 2012, was instrumental in Bayern's 2012/13 Bundesliga, UEFA Champions League and DFB Cup treble win, hitting 22 goals in all competitions.
The Croatia international, now of Juventus, scored a further 26 goals under Pep Guardiola in 2013/14, before leaving for Atletico Madrid following the arrival of Robert Lewandowski.
Another classic target man with the aerial prowess of an old-fashioned centre-half, Wagner's recent goal-scoring record is no less impressive.
The former Werder Bremen, Kaiserslautern and Hertha Berlin striker scored 14 goals for promoted Darmstadt in 2015/16, 11 for Hoffenheim last term and has struck four times in 11 top-flight outings so far this season.
The 30-year-old also netted five goals in seven senior internationals in 2017.
"It's great that Sandro's now playing for us," Martinez said. "He's definitely one of those players you'd rather be playing with than against!"
Watch: Sandro Wagner's top three Bundesliga goals
Martinez and Wagner are part of Bayern's 25-man squad currently warm-weather training in Doha, Qatar.
The Bundesliga leaders resume their title defence away to Bayer Leverkusen on 12 January (kick-off 20:30CET/19:30GMT).