"It looks as if Danny will be going to Middlesbrough - it's difficult for us to compete with their money," Warnock told the Croydon Advertiser.
He added on Sky Sports News: "Danny is a good player and I know he has got one or two offers, which I'd expect for a player of his quality."
Warnock saw Serbian trialist Goran Maric score in Thursday evening's 4-0 friendly win over Boreham Wood and confirmed he is looking to sign a striker with a physical presence.
"I need a taller, bigger lad to start with," commented Warnock.
"We will have to see in the next few weeks when we probably come back from America as to what's available and what we're going to go for.
"We need a bit of luck, like anybody else."