Sergio Aguero has told Manchester City to learn lessons from Paris Saint-Germain's shock Champions League exit to Manchester United.

City are in a strong position in their last-16 tie with Schalke, leading 3-2 thanks to late strikes from Leroy Sane and Raheem Sterling in the first leg.

Pep Guardiola's side are among the favourites for the title but need to complete the job when Schalke visit Manchester for the return game on Tuesday.

And City's all-time leading goalscorer Aguero thinks City must be on their guard following United knocking out PSG and holders Real Madrid falling to Ajax.

"Looking at the recent results, we have to be very careful," Aguero told ESPN. 

"We saw strange things happening this week and it helps us to know that we must be very focused on how we handle our game next week at home.

"[There were] so many unexpected results. PSG had a good lead after winning in Manchester and you saw how United advanced.

"The Champions League is very difficult, all teams are very good. In a long competition like the Premier League you can allow yourself some mistakes but in the Champions League you can't.

"You have to be very focused, be very careful with set pieces and on all the small details."

The final of this season's Champions League is being played at the home to Aguero's former club Atletico Madrid.

"Special motivation? Of course," Aguero added. "It's at the Wanda, I've never played at that stadium.

"Madrid is a city I love very much, my son was born over there. And it's where I started my career in Europe. I will do my best to be there."

Aguero knows more than most that the race for the Premier League title can go right down to the wire, having hit a dramatic late winner to seal the crown in 2012.

Beating Watford at home would move City four points clear at the top, with Liverpool not in action until they welcome Burnley to Anfield on Sunday.

"I learned during my years here that the title of the Premier League is always decided at the end," he added. "There are some exceptions like what happened last season when we won the league a month and a half before the end. But I don't think this will happen any time soon.

"We made history getting 100 points, it's a difficult feat, not easy to repeat something like that. In my eight seasons in the league, I remember that six of them were very close until the last weeks.

"Obviously we are in a great shape right now after coming back from a big points disadvantage against Liverpool. We knew that the key game to win was the one we played against them and from that moment we started to narrow the gap.

"We needed to win for them to see that we were pushing back. Now we are top and in a great position over Liverpool."