The England international has been linked with a move away from Anfield all summer, with a return to former club Newcastle mooted as a possibility
The 23-year-old has struggled for the most part with both form and fitness during his 18-month spell on Merseyside so far, but Keegan is just as worried about the potential knock-on effect it could have on Newcastle if the player were to rejoin the club.
"If you sign Andy Carroll for Newcastle, then what happens to Papiss Cisse and Demba Ba?" Keegan told Goal.com. "For Liverpool, replacing Andy Carroll, what other forwards have they got? [Luis] Suarez is not really a center forward and I think they've got to be careful there."
Carroll isn't the only big-name player to have been linked with a move away from Merseyside this summer, and center back Daniel Agger has been the subject of strong interest from league champion Manchester City.
Keegan, however, has stressed the importance of holding on to your best players and believes the club should keep hold of the Danish international.
"I do, not only because he's a very good player and his partnership with [Martin] Skrtel is very good, but if you sold him, who do you replace him?" Keegan explained. "Who else are you going to find that knows the league as well as Agger and who consistently performs like Agger does?
"The answer is that it's not going to be easy. You don't want to sell your best players, you want to try and improve by keeping your best players and selling on the ones that you don't want. Well, when you look at the players that they've got there, they need to improve by playing together more."
"They've got [Pepe] Reina, although he had a poor season last year, is a world-class goalkeeper and you've got Agger and Skrtel, then you've got [Steven] Gerrard and Suarez - there's five players that you can build a team around."
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