Let's see what the FA Cup rules have to say...
http://www.thefa.com/~/media/776FDC2C663A48568FC3688FA667463A.ashx/01%20FAC%20rules%202009-2010%20_blue_.pdf15. PROVISIONS CONCERNING PLAYERS
(a) Each team participating in a match shall represent the full available strength of each
competing Club.
(b) (i) Each Club must provide a list of names of players taking part in the game (including
the names of the substitutes) to the Referee and a representative of their opponents
in the presence of the Referee at least 60 minutes, in the Competition Proper or any
match in the Qualifying Competition that is being televised live, and 45 minutes in all
other matches before the time of kick-off (the “Official Team Sheet”). Any Club failing
to do so will be liable to be fined by the Professional Game Board a sum not
exceeding £100.
(ii) Should any nominated player or substitute sustain an injury after the submission of
the Official Team Sheet to the Referee and before the kick-off, he may be replaced
without fine if he is injured warming up after the exchange of the Official Team
Sheet, provided the Referee and opponents are informed before the commencement
of the match.
(c) A maximum of seven substitutes may be nominated. A Club may at its discretion use three
of those seven substitute players at any time in a match. Substitution can only be made
when play is stopped for any reason and the Referee has given permission. Prior to the
substitution being made the Club must identify to the Match Officials the number of the
player out and the player in, in accordance with the Official Team Sheet.
(d) All players shall be qualified as players according to the Rules of The Association.
(e) A player shall not play for more than one Club in the Competition in the same season.
(f) All players must have been eligible to play in the original tie in order to play in a replayed or
postponed match; however a player who has been suspended according to the disciplinary
procedures under the Rules of The Association may play in a postponed or replayed match
after the term of his suspension has expired.(g) A substitute who does not play in a match is entitled to play for another Club in the
Competition in the same season.
(h) In all Rounds of the Competition a player shall be a “registered player” of his Club under the
Rules of the Competition.
(i) (i) A “registered player” is one who is either, in the case of a player under written
contract, registered with The Association or, in the case of a player without a written
contract, registered with a League in which his Club competes in the current season.
Any such registration must have been received and accepted by The Association or
League by 12 noon on the Friday previous to the date fixed for playing the Round,
and the registration must be continuous through to the date of the match. .
(ii) In order to be eligible to play in the Final, the players must have been correctly
registered and eligible for the Semi Final Round of the Competition.
(iii) An International Transfer Certificate for Players coming from overseas associations
(including Wales, Scotland, Northern Ireland and the Republic of Ireland) takes
precedence over a Player’s registration. Therefore, this is also required by 12 noon
on the Friday previous to the date fixed for playing the Round for the Player’s
registration to be valid.(j) Temporary (loan) Transfers
(i) A player on a temporary (loan) transfer is ineligible to compete in the Challenge Cup
Competition unless permission to do so is given by the lending Club in writing and a
copy is received by The Association by 12 noon on the Friday prior to the date fixed
for playing the Round. Any permissions must clearly state that the player has
approval to play in The FA Challenge Cup Competition. A registered Trainee or a
player who is registered on a Scholarship for work experience may play for another
Club, subject to written permission being given by the Club that he is registered to
and provided that such permission is received by The Association by 12 noon on the
Friday prior to the date fixed for playing the Round. The Association will not give
permission for players on loan or work experience to play against the lending Club.
(ii) A player recalled, at any time prior to the date of the Round, to his original Club from
temporary (loan) transfer, in accordance with the terms of the loan agreement, may
represent his original Club. Such player may only play in postponed and replayed
matches if he had been recalled in time for the first match in accordance with subparagraph
(i) above and (iii) below as applicable.
(iii) A player on temporary (loan) transfer is eligible to compete if transferred by the
lending Club to the loaning Club after the date and time for player qualification for a
round but must have been eligible to play in the original tie.
(iv) Players on season “long term loan agreements”, are not considered “loan” players for
the purposes of the Rule, and are therefore eligible to play in the Competition.