While some select clubs have been wafting the chequebook, particularly at League One level, many others, including Rotherham, have been operating in a difficult marketplace and are having to be patient.
United finally made their first long-awaited outfield signing of the summer on Tuesday when they brought in ex-Millwall utility man Shane Ferguson.
Activity could pick up shortly, in both an inward and outward direction with midfielder Matt Crooks set for a move to Middlesbrough. He will undergo a medical later this week.
Warne is targeting several more incoming additions with the start of the EFL season being just two-and-a-half weeks away.
He said: “It’s been the strangest one (summer window).
“There has been a lack of movement from the top. Maybe because of the Euros, maybe because of Covid.
“The whole filtering down of players hasn’t seemed to have happened. There hasn’t been loads of big loans yet.
“Even when Charlie Wyke went to Wigan, it didn’t happen at the start of the off-season, it took forever; the same with (Stephen) Humphrys going to Wigan. Everything has taken so long. Some of the big (League One) clubs go in for one player but also another five.
“You speak to the agent of one of those six and it’s: ‘Well, we’re linked to another club and the player really wants to go there.’ Everything has taken longer.
“Maybe everyone was enjoying the Euros or maybe the Premier League clubs haven’t wanted to loan out players yet because all their best players have been on international duty.
“It has been harder this year to add strength to my squad than in any other year.”
Despite a number of clubs being forced to operate amid tough conditions, Warne believes that League One will be a ‘formidable’ division in 2021-22.
Warne, seeking to make it a hat-trick of promotions straight back to the Championship, added: “This does look a pretty formidable League One this year.
“There are quite a few teams with aspirations of doing well. I don’t want talk our aspirations down, but there are some clubs throwing real money about for players. I’ve been gazumped a couple of times. That’s fair enough.”