Boss Zak Brown said before departing Monza that he thinks it is "likely" the Spaniard will sign a new deal for 2018, so long as McLaren dumps Honda and switches to Renault power.
Alonso told Spain's Antena 3 broadcaster the day after the Italian Grand Prix: "McLaren is in a difficult situation because for three years it has been very uncompetitive.
"I think three years of not being competitive is the limit for a team like McLaren - one of the best in F1 history. Starting next year, I think it's going to change.
"I don't know what will happen, but I'm very optimistic. One option is to change the engine. I will wait for their decision before taking mine.
"I want to be loyal to the team as we have been through difficult times together. When they decide and they know the package they will have, I will make a decision."
The 35-year-old said that he expects to know of McLaren's decision "this week".
When pressed about his desire to remain 'loyal' to McLaren, Alonso continued: "I'll give them a chance. We have shared very hard times together.
"I feel part of the team and I think they deserve it."
Alonso has picked up 10 points for McLaren so far in 2017.