Oilers coach Dave Tippett was asked after the morning skate why he decided to put the two forwards on the same line as McDavid, who has led the NHL in scoring in two of the past three seasons.
"Housewarming gift," Tippett said.
Mike Green will also play his first game with the Oilers after he was acquired in a trade with the Detroit Red Wings on Monday for forward Kyle Brodziak and a conditional fourth-round pick in the 2020 NHL Draft or 2021 NHL Draft.
Athanasiou was acquired in a separate deal with the Red Wings on Monday with forward Ryan Kuffner for forward Sam Gagner and a second-round pick in the 2020 NHL Draft and 2021 NHL Draft.
Athanasiou is in the final season of a two-year contract and can become a restricted free agent July 1. The 25-year-old forward has 24 points (10 goals, 14 assists) in 46 games this season and is an NHL-worst minus-45.
"Any team that's willing to make a trade for somebody and show interest, it's obviously a good feeling," Athanasiou said after participating in the morning skate at Honda Center. "I'm just excited to be here."
Athanasiou said he watched a lot of Edmonton games this season and doesn't expect to alter his style much to fit in with McDavid, who entered Tuesday tied for third in the NHL with 84 points (31 goals, 53 assists) in 56 games.
"With my speed, I'll be able to open up a little extra ice," Athanasiou said. "Give [McDavid] time and space and let him do his thing."
Ennis was acquired from the Ottawa Senators for a fifth-round pick in the 2021 draft.
The 30-year-old Edmonton native can become an unrestricted free agent July 1. He has 33 points (14 goals, 19 assists) in 61 games this season.
"I'm ecstatic to be an Oiler and I can't wait to move forward with these guys," he said. "I'm just going to try to shake off some rust and work hard. That's all I can control is how hard I work and compete."
