MUFC finally started a women's side in 2018 after years of criticism that one of the world's biggest football clubs did not have a women's team. But Casey Stoney's side have made strong progress since and currently sit top of the Women's Super League after six games.
However, despite Rapinoe's USA teammates Christen Press and Tobin Heath joining the club in the summer, the 35-year-old OL Reign player clearly still feels Man United held back far too long.
"I think women's football in England is the same as in America - it is so far behind because of what we've had to overcome in the lack of investment," Rapinoe told the BBC.
"It's 2020. How long has the Premier League been around? And we're only just seeing a club like Manchester United put effort and pounds towards a women's team? Frankly, it's disgraceful."
Many would echo the feelings of Rapinoe that, given the amount of cash sloshing around the top Premier League clubs, it was odd that the Glazer owners took so long to invest in a women's team.
The line from United was always that when they did it, they wanted to do it right - and to the club's credit Manchester United Women have made progress every season.
There is little to dispute in Rapinoe's words, but her choice of target does seem a bit odd in terms of timing. Even if United have (undoubtedly) taken too long, at least the effort is there at last.
The stark comparison is with arch rivals Liverpool. While Jurgen Klopp's side won LFC's first league title in 30 years last season, Liverpool FC Women were relegated from the top flight with only one win from their 14 completed games.
So many feel while United are, belatedly, heading in the right direction, the lack of investment in Liverpool's women's side is perhaps worth greater scrutiny.
Elsewhere Rapinoe, who won the Golden Ball for best player as the USA won the 2019 World Cup, told the BBC about her own frustrations. The coronavirus pandemic has meant a lack of women's club football in the US in 2020.
"I've had a few teammates go abroad and play, while I'm training and trying to keep fit in the hopes that eventually we'll be out of this hellscape," she told the BBC.
"I want to keep playing. I'm definitely not anywhere near retirement - I absolutely want to play at the Olympics.
"After the Olympics, I'll have to take a longer look at the next three years. We're a year closer to the next World Cup and it's pretty enticing. We'll leave that one out in the open."
All imagery: PA Images
Chosen for YouChosen for You
Most Read StoriesMost Read