Gary Neville is full of praise for Manchester City's performances this season - but has warned of challenges ahead.
Pep Guardiola's side have enjoyed the best start of any side in Premier League history, picking up 28 points from their first 10 fixtures and sitting five points clear at the top of the table with a +29 goal difference.
However, in each of the last two seasons City have picked up 2.3 points per game between August and October - only to see that drop to less than 1.8 points per game from November to January.
And Neville says Guardiola must avoid a repeat of that winter slump again this season.
"They are at an outstandingly high level," he told Monday Night Football.
"They can only stop themselves. I mention the words robustness and resilience. I look at the winter months and it seems like an old cliché - can you go away to Stoke and that sort of garbage - but there's a little bit more to it than that.
"If you look at Manchester City's last two seasons, one under Manuel Pellegrini and one under Guardiola, and you look at November, December and January. They probably would have won two titles in those two seasons if they'd have maintained their championship-winning level.
"If they drop to that level in November, December and January again then they'll be in trouble. Those months are tough, the toughest months, I don't care what anybody says.
"It's the toughest months to play football - the games, the weather, the injuries, the stockpile of fixtures, the Champions League, the Christmas period…
"Can they get through to February, March and April when the weather gets better again and it's an easier time of year to play football?
"My view is that has cost them in the last two seasons and if they can get through those three months then it could be one of the most outstanding performances. It is brilliant to watch, a great level of football."
Neville pointed out that City face tough games against Manchester United and Tottenham in December before travelling to Newcastle and Crystal Palace in their final two fixtures of 2017.
And he says some of City's young players will need to prove their mettle during a demanding run of games.
He added: "When I played, Sir Alex Ferguson would send home Cristiano Ronaldo, Nani and Anderson around Christmas time for a week just to relive of them of a period that they weren't used to.
"He used to sit them back because it's a tough period for young players in particular, the ones who haven't been there before.
"They've got a bit of experience in that team, but those are the months that will be the test. I'm not saying they can't get through it because I think they're playing at a level whereby they should be able to beat anybody.
"But Pep Guardiola will know what's cost the team in the last two seasons. He'll know it's the November, December and January runs - and they are coming into that now.
"The test is to come, but at the moment they are reaching a level which is quite incredible and brilliant to watch."