United are poised to make the final offer of £3m, one million short of Watford’s £4million valuation.
Ashley believes it is a reasonable price for a player who has little experience in the Premiership.
He made a few appearances in the top flight as a 19-year old.
United offered £2.5million earlier in the week but Watford continue to hold out for more.
The 25-year-old can play at either centre-back or full-back.
Watford are set to include Mariappa in their squad to face Spurs in the FA Cup fourth round tonight ... but he is already cup-tied ... having played in the 3rd round tie against Bradford City.
The player is understood to want a move to Newcastle, and could do what Andy Carroll did last season and ask for a transfer.
He is under contract, so there is no saying he will get what he wants, but (as always in these situations) who wants an unhappy player?