It is the second time that the injury has flared up whilst officially on international duty – the previous occasion being back in March when it was hoped that he would soon be back playing for Wanderers in League One.
Although he finished as Bolton’s top scorer with 21 goals in 49 appearances across all competitions, he missed 12 games between the 2-1 win against Wycombe on February 13 and1-1 draw with Portsmouth on April 13, during which time the Whites lost significant ground on the automatic promotion spots.
Charles became the first Wanderers striker since John McGinlay to score 20 times in consecutive seasons but struggled to shake-off the injury completely and was still managing discomfort with injections by the time the play-off final came around in mid-May.
He lasted just 66 minutes at Wembley and was substituted for Cameron Jerome.
Eoin Toal remains with the Northern Ireland squad, who take on Spain tomorrow night in Mallorca.
Meanwhile, Wanderers have announced another fixture on their pre-season schedule, with a game against Championship side Middlesbrough at Bishop Auckland FC.
Ian Evatt’s side will head to the North East to meet Michael Carrick’s Boro, who finished eighth last season in the second tier and also met Bolton in the Carabao Cup.
Bishop Auckland play at the 1,950 capacity Heritage Park, a stadium opened in 2010 which also provided a temporary home for Darlington FC between 2012 and 2016.
The ground has 500 seats and is situated in Tindale, about a mile-and-a-half from the town centre.
Ticket information has not yet been announced but the club has confirmed an allocation will be put on sale soon.
