FIFA have told the Blues that Paraguayan Ãngel MartÃnez will not be allowed to play in reserve games while he is on trial at Portman Road. Town had planned to take a look at the 21-year-old central defender in match action during Wednesday's second string game at Watford (KO 7pm).
Boss Joe Royle is disappointed that the former Tacuary, Racing Club, Olimpia and Nacional player will not be able to play in any games while with Town: "It is better to see these players in action rather than just in training. The FIFA rules say they have to be signed, but we don't like signing players until we have seen them play, so really it is a restriction of trade.
"It is hard to tell what they are like but we will learn more this week when we have a full week with them."
Town's other trialist, Monaco man Jimmy Juan, is contracted to the French league club and is also unavailable for matches during his time with the Blues.
A number of senior players are likely to be involved at Vicarage Road, partly due to the U18s playing their FA Youth Cup fourth round tie at Stoke on the same night.
Pablo Couñago, Scott Mitchell and Dean Bowditch are all likely to get a run-out against the Hornets but Drissa Diallo is still a couple of weeks away from action after his hamstring injury.
The youths have injury concerns regarding keeper Shane Supple (heel), England U17 striker Darryl Knights (hamstring) and defender Michael Synnott (groin).
Town's youngsters defeated Portsmouth in the previous round, while Stoke surprisingly beat Manchester United.