The 32-year-old is enjoying a welcome return to form in Washington, with seven goals netted in 15 appearances.
Rooney is now chasing down a spot in the 2018 MLS Cup Playoffs, with Schweinsteiger talking up the forward's form ahead of Sunday's reunion.
The Chicago Fire star said: “He’s a huge impact for D.C.
“I think also it helped them a lot to play in a new stadium. They made some changes as well. They really play well, I like watching them a lot and hope it’s going to be a good game for us.”
World Cup winner Schweinsteiger, who spent the best part of two years alongside Rooney at Old Trafford before making his own MLS move, added: “He’s a great player.
“For me, he understands the game really well and he’s always a threat for the opponent, and we have to keep an eye on him, definitely. But, also of course they have other players there that are also really good and can decide games.”
Schweinsteiger has been dropped back into defence for the Fire, having spent much of his career in midfield, so could come into direct competition with Rooney in his latest outing.
The German is looking forward to the challenge, having tangled with a record-breaking frontman in the past during his time at Bayern Munich.
“I remember once we played with Bayern at United and he made a dive in the last minute because I had a yellow card, and I got a yellow-red card,” said the 34-year-old.
“So the first thing I did when I came to United, I thanked him again for that. Off the field we played golf with each other, that was always fun. We had a good time in Manchester.”