The center did not play in four of the final five games of the regular season, including the last two, because of a lower-body injury.
"I want to play every game," MacKinnon said Sunday. "… It was nothing major, I just wanted to be healthy come Game 1, so got some rest, some good treatment, feeling good."
MacKinnon was second on the Avalanche with 65 points (20 goals, 45 assists) in 48 games, behind forward Mikko Rantanen, who scored 66 points (30 goals, 36 assists) in 52 games. MacKinnon scored 25 points (nine goals, 16 assists) in 15 Stanley Cup Playoff games last season; Colorado was eliminated by the Dallas Stars in seven games in the Western Conference Second Round.
"To have him from the start of the series would be what the doctor ordered," Avalanche coach Jared Bednar said Saturday. "It's huge. I mean, it is obvious he's one of our stars and a guy that really looks forward to this time of year.
"... We saw what he can do in the playoffs last year. He took his game to a whole new level, and to have him out there leading us with [Gabriel Landeskog] and Mikko I think would be ideal, and it's something that we need, and he's such a big part of our hockey team, especially driving our offense."
Bednar said forward Brandon Saad and defenseman Conor Timmins could return. Saad missed the final 11 games with a lower-body injury; Timmins sustained an undisclosed injury in a 5-1 win against the Los Angeles Kings on Thursday.
"We'll look at St. Louis, what we project of their lines, see what we like for our matchups, at least to start, and keep evaluating on a day-to-day basis," Bednar said. "Guys might find themselves out of the lineup in Game 1 and possibly be in soon after that. Hopefully the lineup decisions we make, the matchup decisions we make, are the right ones, and even then we'll have to adjust our lineup on a daily basis. There's going to be some tough decisions as we get healthy."
Defenseman Bowen Byram is improving in his recovery from an upper-body injury but will not be available to start the series. He has not played since March 25.
"He's getting better every day and is now skating with the team, which I think is going to help him a lot," Bednar said. "… Now he's feeling a lot better and he's on the mend, and the next thing for him will be getting into skates like this with a lot of guys and taking contact and we'll see where he gets to. He's missed a significant amount of time for us, but we're trying to get him back up to speed and hopefully he's an option for us at some point."
Colorado won the Presidents' Trophy with the best record in the NHL and will have home-ice advantage throughout the playoffs, beginning with the best-of-7 series against St. Louis.
"I'm proud of our guys for the work they've put in," Bednar said. "… One of our goals over the last few years has been to try and get home ice for the playoffs and finish first and have that type of regular season that we can be proud of. I think with all the adversity and just the way this year has gone with injuries and COVID breaks and whatnot, I think it's a nice feather in our cap to be able to get the Presidents' Trophy and set ourselves up for home ice in the playoffs."
MacKinnon said, "I think for everybody it's just getting the chance to win the Stanley Cup. Every year it feels like we're a little bit closer, getting better and better as a team (general manager) Joe [Sakic] has put together. I felt like last year was the first year we had a really, really good chance in the bubble, and this year it feels the same. Obviously it doesn't mean anything, we're playing an amazing team. All we have to do is focus on Game 1 and hopefully get a win tomorrow night, and keep going from there."
NHL.com independent correspondent Rick Sadowski contributed to this report
