Romero, who got a rare start in United's 1-0 home win over Watford on the final day of the Premier League on Sunday when first choice keeper David de Gea was rested, is certain to be going to his third World Cup finals in Russia next month.
However, the 31-year-old could face stiff competition from uncapped River Plate goalkeeper Franco Armani, who was included in coach Jorge Sampaoli's 35-man provisional squad on Monday after a stellar season that included 11 clean sheets in his last 15 matches.
"I have never felt the weight of being inactive," perennial club reserve Romero told Reuters in an interview. "For me it's not the same for a goalkeeper to lack matches as it is for an outfield player.
Despite criticism over an inability to hold down a regular first team place at Sampdoria, AS Monaco and Manchester United in the last five years, the former Racing Club custodian has won an Argentina goalkeeping record 94 caps since his 2009 debut.
"Thankfully, I have shown over the years that whether I play or not (for my club), I'll always be fit because that's what I train for," said Romero, who helped United win last season's Europa League, a competition in which he was a regular starter.
"I have shown I am worthy of playing in the Argentina national team," said the 1.92-metre Romero, affectionately nicknamed 'Chiquito' (little one), who relishes every call-up knowing he is more than likely to play.
"I'm always keen to join up with the Argentina team to play, to stop shots, that's my goal and always has been since Diego (Maradona) gave me my debut."
Romero believes Sampaoli will resolve problems affecting Argentina's recent form which included a nervous run-in to the South American qualifiers last year and a 6-1 roasting by Spain in a Madrid friendly in February.
"We need to put in lots of training to keep growing as a team and gain in confidence and belief in the coach's tactics to get to the World Cup in the best shape possible and win the first match which is important to start on the right foot."
LET THEM WORRY ABOUT US
Argentina kick off against Iceland on June 16 before also meeting Croatia and old rivals Nigeria in Group D.
"We know Iceland have strong players who had a great Euro taking their team to historic new heights and who won't give anything away at a World Cup," Romero said.
"But we, as Argentina, such a football-mad country and so sentimental, have to look inwards and not at other teams. We've got to do our work and if we do that well, the other teams will have to worry about Argentina."
Having had to adapt to three different coaches since they reached the 2014 World Cup final, which they lost 1-0 after extra time to Germany, Argentina were in danger of a faux pas as they sought to settle into Sampaoli's all-out attacking tactics.
"When you get a match like Spain, lots of things are put in doubt but if we trust in the class of players we have, the coach's ideas will show clearly," said Romero, who was injured conceding Spain's opening goal and made way for Willy Caballero.
"Things didn't go as we expected from the start and going home with a 6-1 defeat was not at all nice but we know it's good this happened in a friendly which is when you try out tactics and players, something you have to do with a World Cup close.
"A kid playing (for a club) in Argentina that you want to see how he responds in an international match could turn out to be excellent and you find a fundamental piece (for the team)."
(Reporting by Rex Gowar; Editing by John O'Brien)
