Fer moved to Swansea on loan from QPR during the January transfer window, and he has impressed while with the Welsh side.
And Guidolin said: "Leroy has been a good surprise.
"I didn't know him before but he has helped the team in the last part of the season, he is a good player and it is possible he stays here.
"He is an option. I don't know if he wants to stay, I think so, but he could be a good option to stay."
Fer only has one year left on his contract at QPR, and the London club are unlikely to stand in his way if Swansea do make an offer.
QPR are eager to offload their higher earners this summer, as they look to adapt to life in the Championship
Rangers boss Jimmy Floyd Hasselbaink has already confirmed that he wants to build a young, British squad at Loftus Road, and Fer does not seem to feature in his plans.
Fer has been with QPR since 2014, and he has made 50 appearances for the London club to date.