The World Cup-winning German has been ostracised by the United manager this season, and Can has admitted to being baffled by the situation.
Schweinsteiger, 32, has not played a minute of competitive football under Mourinho, despite being one of the most decorated players in Europe. Can – who has previously played alongside Schweinsteiger at Bayern Munich – cannot understand Mourinho's approach towards the former German captain.
"I know Schweinsteiger very well and I used to play with him," Can said of the out-of-favour United star, according to ESPN. "He's a very good guy and he's a legend. I don't know what happened there but I think they don't have too much respect for him.
"It's a pity because he's a very good guy. He's always somebody who worked hard and is always a gentleman. When I first came up to the first team [at Bayern Munich] he was the first one who came to me and said: 'If you need something come to me.' That was a big help. I was very thankful for that and it's something I'll never forget."
Schweinsteiger was recently reintroduced to training with the United first-team, having spent the bulk of the season working on his own at the club's training complex.
Mourinho has also suggested there is scope for the midfielder to reignite his career at Old Trafford.
However, Bayern Munich chief executive Karl-Heinz Rummenigge recently urged Schweinsteiger to seek a move away from United during the January transfer window.
"My wish for him is that he finds a solution once the transfer window opens in January," he said of the United midfielder, according to Bild.