Taylor, who joined the Hornets on transfer-deadline day, is ineligible for Saturday's meeting between his permanent and temporary employers.
Mackay freely admits that is a blow to Watford, with the Hartlepool-born left-back having performed impressively in his last two outings, which resulted in a 2-0 win over Bristol City and a 6-1 success at Millwall.
Taylor rarely featured in Gordon Strachan's thoughts, and made just one substitute appearance against Sheffield United before leaving the Riverside at the end of last month.
But he has been an instant success for the Hornets, and Mackay is already hoping to extend his loan beyond its current expiry date at the turn of the year.
Andrew has been calm and composed, and is someone who looks like he has played a lot of games in the Premier League, said the Watford boss. He has a lovely left foot and a nice balance to his game.
For someone who has only been here a week or two, he has slipped into the group so comfortably and that underlines his professionalism. As the games go on, he will get sharper and sharper. He gives us options other than having to put square pegs in round holes.
While Taylor and Jonathan Grounds left the North-East on loan last month, Senegal international Mickael Tavares arrived on a temporary transfer from German club Hamburg.
The midfielder, who has joined until January, made his debut in the 3-0 defeat at QPR and retained his place for Boro's subsequent victories over Burnley and Reading.
He has settled effectively, despite admitting he thought Middlesbrough were still in the Premier League when he was first informed of their interest.
To be honest, I didn't know they played in the Championship, I thought they were still in the Premier League,
said Tavares.
But when I came I saw that everything is right here to have a good season and everything is Premier League class.
The atmosphere and coaching is great, so I'm happy to be here.
I spoke (to Strachan) and felt the confidence from him, so I was very interested to come here and help the team get into the top league. My wish is to play well and convince the club to sign me for more seasons.
Boro have signed a fourmonth sponsorship deal with Teesside-based pawnbrokers Ramsdens.
Ramsdens have agreed a six-figure deal that will see their name appear on Boro's strip in October, November, December and January.
Source: Northern Echo
Source: Northern Echo