According to Leafs head coach Sheldon Keefe, both Engvall and Muzzin have been cleared to return to action and are expected to be in the lineup tomorrow night against Detroit in the Leafs' preseason finale, which also means that, barring another injury or a setback, both players will be good to go for the start of the season.
It's hard to tell where they'll slot in tomorrow, but if the Leafs intend to roll with Marner and Matthews on the top line, Tavares on the second line and Nylander on the third line, Engvall could see time on either of the middle two lines. An Engvall - Tavares - Jarnkrok line or an Engvall - Kerfoot - Nylander line could make a ton of sense. I'd imagine Nick Robertson will play wherever Engvall does not.