A career decision looms in September when he expects to decide whether to stay at McLaren Honda, a once-powerful team now at the bottom of constructors' standings.
"We have to win", he said when asked what he will do when his current contract expires at the end of the year.
The Spaniard's comments come just one day after McLaren CEO Zak Brown told Reuters, "the executive committee have now given us our marching orders", to find a new power unit supplier if Honda can't turn things around.
When suggested that such ambitions were unrealistic, due to the partnership's current situation, Alonso said: "I mean, you never know, you can not be 100 per cent now in June about one decision for next year that you don't even start to consider".
"We all want to win".
Brown, who replaced Ron Dennis at the McLaren helm a year ago, added: "Our preference is to win the world championship with Honda". I guess for the team, and same for me.
"I want to win, I joined this project because I want to be world champion, and we are not in that position", said Alonso. After three years we are not in that position, so things have to change, for the team. That is all I can say right now. Until I sit down with myself in September, October or whenever, after the summer, I can not say anything 100 percent now.
IndyCar Series driver Fernando Alonso prior to the 101st Running of the Indianapolis 500 at Indianapolis Motor Speedway.
Asked if his Indy 500 excursion had influenced his thinking, he was insistent: "The third world championship is my biggest priority".
"It is the best auto I can drive, the F1".
"But I know that I can jump into any auto, any race, with any tyres, with rules and be competitive".
Liberty's moustachioed chief executive Chase Carey has spoken of wanting four races in the States - ideally adding Las Vegas, New York and Miami to the existing Austin grand prix - as part of an expanded programme rising from 20 to 25.
'I started when the calendar was 16 races, plus the tests, and now we keep increasing the races year after year.
"If the calendar stays 20, 21 [races], this range we know, I will be happy to continue, if it increases like NASCAR, 40 [or] 50 races, it's not for me, it's better for other drivers".
"I will decide what I am doing after the summer, in September or October, but I want to keep some quality in my life".
The 2017 calendar has 20 races but next year will see it grow to 21 with France and Germany returning and Malaysia leaving.
"If there are 25 or 26 racers or whatever maybe it's good in one aspect and bad in other aspects in how demanding your life becomes".