Sergio Aguero has told ESPN that Manchester United's shock win over Paris Saint-Germain is a warning shot to Manchester City in the Champions League.
United produced a stunning comeback on Wednesday, drawing 3-3 on aggregate and winning on away goals at the Parc des Princes to become the first team in European Cup history to win a knockout tie from a 2-0 deficit at home. Ajax, meanwhile, dumped holders Real Madrid out after a 4-1 thrashing at the Bernabeu.
"Looking at the recent results, we have to be very careful," Aguero told ESPN with Manchester City 3-2 up over Schalke ahead of next week's round-of-16 clash at the Etihad.
"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."
City have never gone beyond the semifinals of the Champions League and the competition remains a priority for the club. This year's final is at the home of Aguero's former club Atletico Madrid and in the city where his 10-year-old son Benjamin was born.
"Special motivation? Of course," Aguero said. "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."
Before City's Champions League tie, Pep Guardiola's men have the chance to extend their lead at the top of the Premier League to four points when they face Watford on Saturday and put more pressure on Liverpool.
Liverpool don't play until facing Burnley on Sunday and Aguero expects the title race to go right to the wire.
"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."
