Sam Allardyce believes Everton’s willingness to pay £20m for Theo Walcott is a further indication he will remain manager next season and possibly beyond his 18-month contract.

The Everton manager confirmed interest in the Arsenal winger on Friday, with the club in advanced talks to beat Walcott’s former employers Southampton to his signature. Everton have signed Turkey’s Cenk Tosun this month for an initial £21m. The former Besiktas forward could make his debut against Tottenham Hotspur at Wembley on Saturday.

Everton’s heavy spending follows their record transfer outlay last summer when £140m was invested in seven additions to the first-team squad with poor results. Allardyce, who signed a short-term contract to succeed the sacked Ronald Koeman, believes the hierarchy’s financial commitment to his January aims is evidence he has a long-term future at the club.

Asked whether Everton’s spending strengthened his conviction he would be the manager next season, Allardyce replied: “Yes. In my opinion I came here on a short-term contract because it suited us both, which doesn’t mean to say it won’t be a long-term tender because a contract for me doesn’t matter that much.

“If it was a longer contract it would still have the same pay-off. If it were four years it wouldn’t have a four-year pay-off, it would have a short one. I’m happy with a short pay-off because both sides need to know where they are going. If I’m not satisfied with them, I want to leave and if they’re not satisfied with me, they want me to leave. The equation is quite simple then because at my time of life I want that relationship with a football club.

“My relationship with a football club only grows by me growing the football club on the pitch and getting results. That keeps me in a job. If those results don’t go well, I accept that puts me under pressure and I leave and that’s fine.”

Walcott, who has 18 months remaining on a £110,000-a-week contract, is considering his options – staying at Arsenal is one – with Everton and Southampton keen to offer the 28-year-old the fresh start his career needs. Allardyce sounded hopeful of luring the player.

“He knows me, he knows Sammy [Lee], he knows Craig [Shakespeare] and he knows Martyn [Margetson, Everton’s former England goalkeeping coach],” he said. “He knows us and I think we can deliver a new stadium in his time here. The club is moving forward in the right direction. The overall future of the club is why I am here because the future looks good. I have to balance that progress off the field with progress on it.

“At this moment in time he is the right age with the right experience to make an impact on Everton Football Club. He is the prime age for a player in today’s Premier League world and because of all the experience and knowledge he has gained he should be at the peak of his career.”

Allardyce confirmed he also wanted to sell this month and that the £23.6m summer signing Davy Klaassen could follow Ross Barkley and Kevin Mirallas out of the club.