The 34-year-old winger signed a 12-month deal in February and Jol is considering whether the Irishman has the legs to keep playing at the top level.
"A few years ago they told me he was quite old - he was 33 - and he's still playing, so I don't know [how long he can go on for]," Jol told the Fulham & Hammersmith Chronicle.
"It was the same with Danny Murphy. Every year they gave him another year, but he was 35 and still one of our best players.
"He's a true professional. What we will do for him is give him an extension if we feel he can play for another year."
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