The pair went their separate ways this summer, but the Paraguayan forward has admitted his gratitude to Hargreaves for helping him to settle.
"When I arrived in Germany I started speaking with Owen and English was the first language I learned," Santa Cruz told The Sun. "For six months I only spoke English and then the boss stepped in and told me to speak German.
"Speaking English has really helped me settle here. Owen has made it much, much easier for me.
"It has helped me get closer to the players. You can understand jokes and feel part of things.
"Myself and Owen are great friends. Owen recommended Blackburn and told me I'd be happy here."