Formula 1 arrives in Monza for the Italian Grand Prix at the start of a month that will prove key for defining next year's driver line-up.

At stake are the careers of experienced veterans like Jenson Button and Felipe Massa, plus the fate of rising stars like Stoffel Vandoorne and Esteban Ocon.

With the futures of so many drivers interlinked, it is hard to know what the trigger point will be to kick things off, but it is pretty clear that things will have to start soon - and may well get underway at Monza this weekend.

September is the time when many driver options expire, which means teams are ultimately forced to decide whether they want to commit to one of their current men or let him become available to the open market.

Three teams keeping out of this are Mercedes, Red Bull and Ferrari, who have all confirmed their line-ups for 2017.

But outside that trio, the one man a lot of teams are keeping an eye on is Vandoorne, whose option at McLaren is understood to lapse towards the end of this month.

The Belgian is widely expected to get the nod to join Fernando Alonso next year in place of Button, but no final decision is believed to have been signed off just yet.

For rival outfits that are interested in taking Vandoorne if McLaren are, as Toto Wolff said, 'crazy enough' not to take him, it means they will not want to close off opportunities just in case he becomes free.

Renault team principal Fred Vasseur is known to be a big fan of Vandoorne's, and would almost certainly jump at the opportunity to land his services if he is available. But Vasseur is aware that situations elsewhere are important, and that driver markets normally get sorted in order.

"I think as usual you will fill the grid from the top," he explained. "Now, Red Bull, Ferrari and Mercedes they are fully booked. The next one will be Williams and McLaren, and then we will have a clear view of the situation.

"I would also like to see the improvement of my guys, as I think we are on a good way."

That means Renault will likely keep its line-up open until it knows what Vandoorne – and equally what Valtteri Bottas and Sergio Perez are up to.

Bottas' fate is in the hands of Williams, which holds an option on him that it also believed to run out this month. And while all indications point towards Williams taking it up, until a new contract is officially signed, nothing can be guaranteed.

Confirmation that Bottas is to remain means there will still likely be one seat available at Williams, with Massa not expected to stay.

For Perez, the situation is still unclear. The Mexican has openly hinted that his sponsors may want him to move on next year, but there are suspicions that the situation is being stirred up to help him secure better terms for a revised contract at Force India.

Force India has repeatedly said it would be surprised if Perez departs.

The fates of Vandoorne, Bottas and Perez will have huge implications on who goes elsewhere, as there will then be a scramble by drivers to get in the remaining seats.

For veterans like Button and Massa, who could find themselves forced out by their current teams, the choice will be on remaining in F1 with less competitive machinery or calling time on their grand prix careers.

But other youngsters too could benefit. If Perez leaves Force India, then Pascal Wehrlein is favourite to get promoted from Manor to take his place.

If Renault has a seat available, then Ocon will have a good chance of landing it if he continues to impress at Manor over the remainder of the season, while Lance Stroll's name keeps cropping up in F1 circles.

Then there are teams that could stand to gain too: Haas and Sauber could find themselves with some pretty good options if there is a lot of movement elsewhere and some good names have been left out in the cold.

As September starts, we don't know what will be the moment the dominoes of the F1 driver market start to fall, but when this month finishes it will be a surprise to not know how most of the grid will be shaping up for 2017.


Gallery: Analysis: F1 driver market braced for crunch month