Mainoo, earning £20,000 weekly, is reportedly in talks with United over a new contract.
However, Foster believes the 19-year-old could become frustrated when comparing his salary to teammates earning significantly more despite performing at a lower level.
On his Fozcast podcast, Foster emphasised the importance of securing Mainoo’s future with a competitive wage.
“It must really annoy Kobbie Mainoo because he must be looking around at some of the players that are on crazy wages that are nowhere near as good as him,” he said.
“They don’t put in any of the performances that he puts in, and they’re earning three, four, five or even six times the amount he is. I thought that after the Euros, he was going to go on to be a world-beater this season.
“I still think there’s a world beater there as well, and it’s probably mental fatigue or a bit of burnout. I think we will see an absolute player.”
Reports indicate that Mainoo’s representatives are seeking a £150,000-a-week deal, but negotiations may be tough with new owner Sir Jim Ratcliffe focused on cutting costs.
Foster warned that clubs like Chelsea would be willing to meet those demands, which could put United at risk of losing one of their brightest prospects.
Source: ghanasoccernet.com
