Tisdale said: "Ryan's had a tough week and he's been playing the last two or three weeks under the weather.
"You can't promise anything in a transfer window, I'm not looking for anyone to go and Ryan's our player."
Tisdale continued: "He did great when he came on, he certainly showed his commitment and his determination.
We've only had firm offers from the one club, Brighton
Exeter City manager Paul Tisdale
We turned down a couple of bids from Brighton for him but they weren't reflective of what I think he means to us for the rest of the season, so as it stands at the moment he is our player."
Harley, who is out of contract at St James Park in the summer, has netted eight goals for the Grecians this term.
"There are clubs who I suspect have been watching Ryan and other players, but we've only had firm offers from the one club, Brighton," added Tisdale.
Source: BBC Sport
Source: BBC Sport