The goalie, who has missed 23 games because of a knee injury, practiced for a second straight day Tuesday. He has not played since March 19.
"It was another really good day for Fred today," Toronto coach Sheldon Keefe said. "He feels real good coming off the ice here today so the plan is for him to start tomorrow against Ottawa."
Andersen has spent the past seven weeks working to rehab the injury, which included a conditioning stint with Toronto of the American Hockey League last week. He allowed two goals on 14 shots in 30:52 of a 5-3 loss to Manitoba, the Winnipeg Jets' affiliate, on Thursday before allowing four goals on 38 shots in 64:32 of a 5-4 shootout loss to Manitoba on Saturday.
"I tried to push it a little bit, push the intensity a bit," Andersen said Saturday. "I thought the intensity got better and better as the game went on. Playing hard on every puck. And just trusting to have energy to play the full game. It was great to have some game action and play around with it and definitely work on how to have the right mindset."
The Maple Leafs (35-13-6) clinched first place in the Scotia North Division and will play the Montreal Canadiens in the Stanley Cup First Round. A start date for the series has not been determined.
Keefe has yet to say who will start Game 1 of the playoffs, but said he is not overly concerned about how Andersen played in his two AHL games or how he plays against the Senators on Wednesday.
"Fred's played a lot of games in the NHL, he has a lot of experience," Keefe said. "So we're not going to read too much into any one particular game, just like we're not going to read too much into his AHL conditioning stint. This was all about just him getting comfortable and feeling good when he leaves the net at the end of the day from a health perspective."
The 31-year-old, in the final season of a five-year contract, can become an unrestricted free agent after this season. He is 13-8-2 with a 2.91 goals-against average and an .897 save percentage in 23 games (22 starts) this season.
Jack Campbell has been the Maple Leafs' primary goalie with Andersen sidelined. Campbell is 17-2-2 with a 2.11 GAA and .923 save percentage,
Keefe said he has been encouraged with how Andersen has looked at practice the past two days and is glad Andersen will be able to get some NHL game action prior to the start of the playoffs.
"Giving him those game reps and having him out there as close to playoffs is a positive thing," Keefe said. "He's feeling good. I thought he was tremendous these last couple of days on the ice. He's worked extremely hard to get himself back to being ready. His approach has been really good so it's good to have him back and the guys will be excited to play in front of him."
Forward Nick Foligno, who has missed the past two games with an upper-body injury, practiced on a line with center John Tavares and right wing William Nylander on Tuesday and will be a game-time decision against Ottawa.
Foligno has four assists in five games with the Maple Leafs since being acquired in a three-team trade involving the Columbus Blue Jackets and San Jose Sharks on April 11.
Defenseman Justin Holl, who practiced on his regular pair with Jake Muzzin, also will be a game-time decision because of an undisclosed injury.
Forward Zach Hyman, who has missed nine games with an MCL injury, practiced on a line with center Auston Matthews and right wing Mitchell Marner but will not play against Ottawa.
Center Riley Nash, acquired by Toronto in a trade with Columbus on April 10, has yet to make his Maple Leafs debut because of a lower-body injury. He practiced on a line with left wing Alex Kerfoot and right wing Ilya Mikheyev but will not play Wednesday.
