"At the beginning of the season, I said they have to sell him. Harry wanted to leave, and he was really disappointed he didn't go," former Lilywhites' man said.
"When you are disappointed you have two choices - to put yourself right and come back on the pitch and play as you need to, or you give up.
"At the minute he hasn't scored the number of goals you would expect.
"For the last few years, he's been the top scorer of the club and the Premier League and at times it's almost looked like he may rather be playing elsewhere.
"In my opinion, Tottenham doesn't really have any choice but to let him leave now at the end of the season."