Wrexham are four points clear of Notts County at the top of the National League with two games remaining after beating Yeovil Town 3-0 on Tuesday.
They can clinch the title and automatic promotion to the Football League, for the first time since 2008, in front of their home fans against Boreham Wood on Saturday.
"I’ll come out of retirement and come and play for @Wrexham_afc next season. I’ll also give my salary to the charity of the fans choosing," Robson-Kanu wrote in reply to an Instagram post by Reynolds after the Yeovil match.
There was no immediate response to the offer.
Wrexham have former England goalkeeper Ben Foster playing for them, with the 40-year-old pulling off a vital stoppage-time penalty save in a 3-2 home victory over Notts County this month.
Robson-Kanu was capped 46 times by Wales and scored a famous goal in a 3-1 win over Belgium in the 2016 European Championship quarter-finals.
He played in the Premier League for Reading and West Bromwich Albion.
