The defender scored his first Gunners goal on his competitive debut for the club as they beat London rivals Chelsea 4-1 on penalties – following a 1-1 draw – to lift the Community Shield.
Signed on a free transfer from Schalke, the 24-year-old Kolasinac was named in the Bundesliga team of the year last season.
He started on the bench on Sunday but replaced captain Per Mertesacker, after he suffered a head injury, and impressed with his strength and aggression.
That came as no surprise to Walcott, who also came on as a substitute and scored Arsenal’s first penalty in the shoot-out, and has been admiring the new recruit in training.
“Honestly, he is an absolute animal,” he said of Kolasinac. “He’s incredible. I see him in the gym every day, you can just tell he looks after himself well, he eats the right food and he’s professional. You can see the power he’s got when he’s got the ball, his pace and everything. It’s beautiful to watch and he’s a great addition to the squad.
“Trust me he’s not easy to get around (in training) – he’s quite wide as well. He fits perfectly for the Premier League, he’s absolutely perfect.
“He’s going to show something different, I’ve seen glimpses of him in pre-season and he’s going to get fitter, stronger and quicker. This league is the best and I think he could be one of the best in this league.”
MK Dons will look to build on their first win of 2018 when they host Bury in a vital clash at the bottom of Sky Bet League One.
Morecambe have paid tribute to former club president Jim Bowen, who died earlier this week aged 80 following a battle with ill health.
Matt Crooks beginshis suspension when Northampton host Rotherham in League One on Saturday.