Pastore was one of PSG's first big-money signings when he joined the club from Italian side Palermo for €39.8m in 2011, but with the Parisians under pressure to sell in order to comply with Financial Fair Play regulations and Pastore having fallen down the PSG pecking order following the arrivals of a host of big-name stars, he looks set to be available this summer.
According to the aformentioned source, West Ham boss Mauricio Pellegrino is keen to bring in the 28-year-old as the first signing of his tenure, with the clubs in talks over a deal that could be worth up to £17.5m already underway.
The Argentine international has made 269 appearances for PSG during his seven years at the club, scoring 45 times, but made just 17 starts during the 2017/18 campaign.
Pellegrini is keen to add high-quality recruitments to the 'Hammers' squad as he looks to instill an attacking brand of football at the London Stadium, with Pastore seen as the ideal man to add the creative edge that West Ham often lacked last season.