The early returns on the Joe Thornton-Auston Matthews-Mitch Marner top line in Toronto were all positive in five games.

Each of the three are at or above a 60 per cent corsi rating at 5-on-5. Marner is tied with John Tavares for the team points lead at six, while Matthews is working at a point-per-game rate even though he's only scored on two of his league-leading 27 shots -- a 7.4 percentage that's well below a 15.5 per cent career average.

In Wednesday's defensive snoozer (which was actually positive in some way for both teams) the Thornton-Matthews-Marner line controlled 75 per cent of the 5-on-5 shots they were on the ice for.

It was Toronto's best line.

And now it's time for a shakeup.

Thornton left Wednesday's game with an injury that Sheldon Keefe described as "not a day-to-day thing." The team awaits the results of an MRI later Thursday for full details, but it's clear Toronto will have to move on without its Jumbo centre-turned-winger for a while.

The question, naturally, becomes: who replaces him on the top line?

And it might not even be quite that simple.

Adding a little more intrigue to the mix is the fact Auston Matthews departed Thursday's practice early, leaving some question as to whether or not he'll be in the lineup for Round 2 against Edmonton Friday.

"He just wasn't feeling great today coming off the game yesterday, so just going to take the rest of the day to see how he is tomorrow. We'll have an update in the morning," Keefe said.

If Matthews is out, then John Tavares' line becomes the new "No. 1" and, really, all sorts of possibilities for line changes enter the mix. But with Matthews, at least, it seems a little more fluid and even if he doesn't go on Friday his absence may only be short term.

The Thornton loss will have the longer-term impact, so who could replace him on the top line with Matthews and Marner?