Millwall manager Neil Harris is looking to add another five players to his squad before the transfer deadline next month.
The Lions made their fourth addition of the close season on Monday when they signed QPR striker Matt Smith.
Harris said: “We still need another four or five players, that’s for sure. We need another goalkeeper, striker, wide player, a centre-mid and possibly another defensive player. We have put bids in and are trying to progress things. We have four weeks to conclude our business and we will.
“We’ve talked about bringing in younger players on loan if they are further down the line than our own. Even they are tough to get in on loan because clubs need to use them in pre-season and no-one plays 90 minutes at this stage. It’s still a difficult period of recruitment, up until the middle of July.”