The 20-year-old Vaakanainen skated with Connor Clifton as part of the third defense pairing during Monday's practice at Warrior Ice Arena after his recall from Providence, and Bruce Cassidy said afterward that it's a game-time decision between Vaakanainen and Steve Kampfer to fill Torey Krug's vacant spot.
The best bet is that it will be Vaakanainen, given his ability to play big minutes, play equally at both ends and move the puck with his excellent skating ability.
Vaakanainen was off to a slow start with two assists in 15 games this season for the P-Bruins and wasn't particularly sharp in training camp this time around for Boston after breaking camp with the team a year ago. Bruce Cassidy also mentioned that the 2017 first-round pick had some work to do with his practice habits, but that's nothing new as young guys like Charlie McAvoy have also gone through that learning curve when it comes to Cassidy's fast-paced practice sessions.
"The 12 forwards will be the guys that were out there and we've got a decision to make on the back end between [Steve] Kampfer and [Urho] Vaakanainen," said Cassidy of Vaakanainen, who had both high and low moments while putting up four goals and 14 points in 30 games last season for the P-Bruins. "He's played better, defended better. I think early on he was getting stuck out wide. I don't know if that's a European-sized rink issue or just an issue because of the way they play over there, but it showed in some goals against where he was getting beaten to the middle [of the ice].
"We need to make sure that is buttoned up if he's in the lineup. He's been moving the puck better and just more engaged in the game. He's been practicing hard too and becoming a better pro, so all good things and his game is falling into place as well."
Here are the projected line combos and D-pairings with both Krug and Jake DeBrusk out for Tuesday night's game against the Panthers, but not ruled out for Friday night's big game against the Maple Leafs.
Click here to download the new MyTeams App by NBC Sports! Receive comprehensive coverage of your teams and stream the Celtics easily on your device.