Morgan believes that Pietersen will be a big influence upon the side.
"Kev offers a hell of a lot as a senior player and as a batsman," Morgan told Cricket365.
"As a senior player he leads by example with the confidence in which he goes about his business. People rub off on that and that's crucial.
"When I first came into the team he was one of the more senior players and he was a guy you could turn to and ask difficult questions or have no hesitation in turning to him for a positive option. In that regard I think he's fantastic to have in the squad and back in for the one-day series."
The first ODI takes place at Headingley on Friday.