One was born into one of Mexico's most prominent families and grew up amid the bucolic delights of Guadalajara; the other raised by parents so desperate for him to help them escape the poverty of Rome's rundown Ponte Dinona district that his father worked nights in a supermarket to free up the days to taxi him to training. On such disparate goalscoring talents do Manchester United's hopes rest in the months ahead. One of the more fascinating aspects of the unfolding season will be to see if either – or both – have the pedigree to do so.

The club's hopes of regaining their title may, in part, depend on one of them. The prospect of Michael Owen being unhindered by injury in the forthcoming season seems as far-fetched as Dimitar Berbatov being a paragon of consistency. That is why Alex Ferguson has already declared that he will be looking to €9.5m new signing Javier Hernandez (he of the pastoral upbringing) and Federico Macheda (the working-class boy who, though 18, will not be sent out on loan) to help out Wayne Rooney.

Hernandez enjoyed the novel experience of playing for both his new club and his old one, Chivas de Guadalajara, on Friday night. He scored for Chivas in the first half, helping them to a 3-2 win over United.

Despite the defeat Ferguson was effusive in his praise for his new signing, calling him "first class" and deeming the goal "a marvellous strike".

One issue Ferguson has to ponder is how Hernandez, known as Chicharito (little pea in Spanish), will fit around Rooney, the Mexican being a very similar kind of striker.

Hernandez's fearless display for Mexico in South Africa – he scored against France and Argentina – should not disguise the fact that just 18 months ago the responsibility of growing up in one of Mexico's foremost football families – his father, Javier Snr, played for Mexico in the 1986 World Cup and his grandfather at the 1954 tournament – all became too much for him.

He found himself languishing on the Chivas bench and his father recalls a breakfast meeting at a restaurant between parents, son and agent, which was supposed to be a discussion on how best to move his football career on, turning into a counselling session.

Only 20, Hernandez wondered if heading back to college might be a better option. "He doubted himself; he doubted he was capable of playing in the first division," said Javier Snr. "As parents, we told him he had to be patient, but as a young player he was impatient. We talked to him about being persistent and in time everything would come."

Father was right. When a starting place came at Chivas he scored 19 goals in 22 games – left-footed, right-footed, long range, drifting wide, staying central, with his head. "He's got some serious hops," is how Chivas forward Jesus Padilla describes the remarkable powers of elevation of a 5ft 9in player.

Hernandez's first three goals for the national side came with his head, elevating him to the kind of celebrity which saw 1,000 fans waiting to sign his shirts when United arrived in Houston. There's already a name for it in the US: "Chicharomania".

It has helped that Hernandez is mature, articulate, telegenic and has been studying business administration at one of Mexico's top universities; factors which have made the Mexican football federation regularly put him on at their news conferences.

Macheda fits the telegenic category, too, though the similarities stop there. His is the story of the impoverished family for whom the discovery of the talented son meant them all, even an initially unsettled 15-year-old brother, upping sticks to a home in Sale, Greater Manchester. Before and since, there have been doubts about whether Macheda has the self-discipline to develop into a talented player at one of the world's biggest clubs.

Sources within the Italy under-21 set-up have wondered about his attitude, and Ferguson hinted at this too at times last season.

The image of Macheda with a bevy of delectable women has been dropped from his Facebook site but his challenge is to show that he is a 90-minute player and not an impact substitute – athough his last season was effectively wiped out with a groin injury – destined only to be remembered for the injury-time strike at home to Aston Villa in April 2009 which was critical to United's League title.

The two players' eye-catching performances in United's impressive 5-2 win over the MLS All-Stars last week suggest that Hernandez, diminutive though he might be, is the more likely to become a lasting force – even in the bracket of Ole Gunnar Solskjaer, another player whom no one made much of when he arrived for £1.5m in 1996 but popped up all over the frontline. Yet Macheda is the one who has shown flashes in the heat of Premier League battle.

"As good a talent as I've seen in a young player as a centre-forward," was Ferguson's rich tribute only four months back, and if he doesn't have the man-management skills to develop Macheda, then no one does. Here are two absorbing stories to follow.