West Ham United are preparing an offer worth up to £25m for Bournemouth’s Callum Wilson after it was confirmed Diafra Sakho will miss up to six weeks with the thigh injury he sustained in Sunday’s 1-1 draw at Manchester United.

Wilson has emerged as Slaven Bilic’s main priority in the January transfer window after a poor start to the season that has left West Ham just one point clear of the relegation zone. Despite spending heavily on the loan acquisitions of Simone Zaza and Jonathan Calleri in the summer, Sakho became the club’s first striker to score a goal this season in the 1-1 draw at Old Trafford on Saturday.

It was the 26-year-old’s second Premier League start of the season after recovering from a back problem but the results of a scan on his injured thigh have prompted West Ham to step up their efforts to sign Wilson in January.

However, Bournemouth are likely to be heavily resistant to any move for their top scorer having rejected a bid of around £15m from West Ham in May. Wilson signed a new four-year contract in July and has also been tracked by Tottenham in the past.

This week the Bournemouth manager, Eddie Howe, dismissed suggestions that the 24-year-old could join Newcastle in January.

“It has got no relevance to us. Not to the football club or to Callum. There’s no substance to the story,” he said. “The only time that will influence him is if he believes it or reads it himself. And I would encourage my players to just concentrate on their day-to-day job.”

West Ham have been scouting Wilson since his 20 goals helped Bournemouth to promotion from the Championship in 2015. He scored a hat-trick at Upton Park in his second Premier League match before being ruled out for the majority of last season with a serious knee injury.

West Ham officials are believed to be in negotiations with Juventus over the structure of the deal for Zaza, who arrived in August on an initial loan. The Italian champions are due a further €20m if he makes more than 14 appearances for the first team, with Zaza so far having failed to find the net in eight Premier League appearances.

The Argentina Under-23 international Calleri, who joined on a season’s loan from the Uruguayan second division side Deportivo Maldonado in the summer, has no goals from eight appearances so far.