The 38-year-old told BBC Three Counties Radio: "We won't be just getting bodies in the door.
"They will have potential. It could be loans from Premier League clubs who we think will improve the team."
Mackay was unsure whether he would be able to make inroads in the transfer market before Friday's season opener at Norwich City.
He was also unwilling to comment on speculation linking the Hornets with young Walsall striker Troy Deeney.
Lansbury wasn't in the Arsenal squad today with younger and more untried players either playing or on the bench, I reckon he will sign on loan tomorrow
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It has been reported the 22-year-old has handed in a transfer request in order to speed up a move away from the Banks's Stadium.
"I'm not going to comment on any players that are signed by other football clubs," said Mackay.
"I think that's disrespectful to them and the football club.
"Until someone is sitting next to me with ink on paper, I'm certainly not going to be talking about them."
If Deeney were to head to Vicarage Road he would face competition from the likes of Danny Graham and Marvin Sordell.
Graham netted the only goal of the game on Saturday as Watford overcame League One side Charlton in a pre-season friendly.
Mackay reserved praise for both of his frontmen: "Danny has been absolutely different class this pre-season.
"He's looked dangerous and has caused teams problems. I think him and young Marvin had a nice little partnership going on.
"There's that little X-factor there with Marvin, he's someone that always gets into a dangerous area during a game."
Source: BBC Sport
Source: BBC Sport