Saints have smashed their transfer record by completing the signing of Roma striker Pablo Osvaldo, for a fee that could rise to nearly £15m.

The 27-year-old forward has agreed a four-year contract at St Mary's and will be officially unveiled tomorrow.

Roma have announced that the sum being paid for Osvaldo is an initial €15.1m (about £13m) plus another €2m (£1.7m) in potential bonuses.

The Italian international therefore becomes the most expensive player in the club's history, eclipsing the fees of around £12m paid for Gaston Ramirez and Victor Wanyama.

According to reports in Italy, Osvaldo has agreed a deal that will see him earn about £50,000 per week.

The player, who previously played under Saints boss Mauricio Pochettino at Espanyol, had been linked with a move to the club throughout the summer.

He took some persuading, though, having initially been reluctant to join the club. But Osvaldo's resistance has now been overcome, and he will significantly strengthen Saints' attacking options.

Osvaldo began his career with Argentine side Huracán, before moving to Italy, with Atalanta, in 2006. After a spell at Lecce, he was sold to Fiorentina and then Bologna, before joining Espanyol in January 2010.

During his 18 months there, he worked with Pochettino, and supporters might remember the forward’s quote about the manager’s training methods that was widely re-publicised following his appointment at St Mary’s.

“He makes you work like a dog. Sometimes you feel like killing him, but it works,” said Osvaldo.

Although Roma paid Espanyol about £15m for him two years ago, and despite an impressive record with the Serie A side, Osvaldo endured a rocky relationship with the supporters and the club’s hierarchy during his time there.

Just last month, it was reported in Italy that directors at Roma were overheard saying they wanted to pressure the player into accepting the Saints deal, after one of them failed to properly hang up following a call from a journalist.

Osvaldo has been at the centre of a number of controversial incidents during his time in Italy. Most recently, he insulted caretaker manager Aurelio Andreazzoli after only being used as a late substitute in the 1-0 defeat to arch rivals Lazio in the Coppa Italia final.

His outburst led to his exclusion from the Italian squad for this summer’s Confederations Cup.

Shortly after his arrival at Roma, he was accused of hitting teammate Erik Lamela in the dressing room after being upset that he had not passed him the ball.

His bad-boy image is not helped by six dismissals in the past three seasons, including matches for both club and country. It has also helped sour his relationship with the Roma crowd.

In another incident, he, along with his teammates and former coach Zdenìk Zeman, had abuse thrown at them by a group of supporters on returning to the train station in Rome following a disappointing 3-3 draw at Bologna last January, with Osvaldo said to be the prime target.

He drew the fans’ ire again a month later, when he wrestled the ball from Roma captain and legend Francesco Totti in order to take a penalty against Sampdoria, only to miss as his side fell to a 3-1 defeat. His car was subsequently pelted with rubbish and eggs.

Even this week, he posted an image on Twitter showing an insulting message that had been spray-painted on the ground in the car park of his home.

However, such incidents can mask the undoubted talent of Osvaldo, who netted 17 times in 31 appearances for his club last season. Osvaldo has also been capped nine times by Italy, starting last Wednesday's 2-1 friendly defeat at home to Argentina, and represents a major coup for Saints.