The FA Women’s Super League was established in 2010 but Manchester United did not form a team until 2018.
The club won promotion to the WSL in their first season and Casey Stoney’s team are currently top of the WSL table after six matches of the 2020-21 campaign.
USA stars Christen Press and Tobin Heath both joined Manchester United over the summer but Rapinoe says English clubs need to do more to support women’s football.
She told BBC Sport: ‘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.
‘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.’
Rapinoe, who helped USA win the Women’s World Cup in 2015 and 2019, also discussed taking the knee during the national anthem four years ago.
She took the knee in support of Colin Kaepernick against racial injustice and police brutality but says she did not feel supported by the U.S. Soccer Federation.
‘Any time I have someone try to explain or argue with me about kneeling or arguing, it’s just an incoherent, fumbling, patriotic mess, right?
‘Taking a knee sharpened my understanding of what I did, how I supported Colin and sharpened my resolved in that.
‘It was not a comfortable time. I certainly felt that at least my international career was a little bit in jeopardy.
‘It showed me a lot of true colours around me in a lot of different ways. The critics yell really loud and I had a federation who clearly didn’t support me and, I felt, a coach who really didn’t support me, but I had so many people around me who always stuck by me and were with me the whole time.
‘But you have a choice of what you do in the world. You just have to be prepared to wear the consequences of your actions.’