Almen Abdi is back in full training after missing Watford's last friendly due to illness but the club are still waiting to conclude assessments on Fernando Forestieri and Craig Cathcart's injuries.
Abdi did not travel with the rest of the squad for Saturday's 2-2 draw with Shrewsbury Town.
And head of medical Marco Cesarini today said: "He had a temperature in the morning and the doctor suggested he should not travel for five hours on a coach. After two days he had recovered and he is training with the squad so we are happy with the decision."
Cesarini also confirmed the 27-year-old has not been suffering with the foot condition which ruled him out for a large part of the 2013/14 campaign.
Fellow midfielder Sean Murray was also absent at Greenhous Meadow due to the ankle injury he picked up against Chemnitzer FC nine days ago.
"Sean twisted his ankle in Austria but it is a minor problem so we expect to have him back in a week. The scan showed positive results," Cesarini said.
Watford suffered two injuries during the match with Shrewsbury. Cathcart was taken off in the first half due to a knee problem and Forestieri suffered a bad cut on his Achilles in the second period, which resulted in the Golden Boys being reduced to ten men with the score 2-0.
Cesarini said: "Fernando has a problem with his Achilles. We will wait for another week and keep an eye on him before we have all the information.
"Cathcart came off with a knee problem and we are still assessing him. That assessment will finish in the next few days."
Watford had hoped to bring Reece Brown back on to the field in place of the injured Forestieri for the final ten minutes but the fourth official refused.
Brown had previously been on the pitch for half an hour after he replaced Daniel Pudil at half time only to be subbed off in favour of first-year professional Josh Doherty on 76 minutes.
Cesarini confirmed: "It was already decided before the game to give 30 minutes to Reece and 15 minutes to Josh.
"Reece knew about it in advance and was fine with it. He was willing to come back on when Fernando was injured but the fourth official wouldn't allow it."
It was also confirmed Connor Smith would feature for the Under-21s tomorrow night at Wealdstone after he had been struggling with a minor injury during the pre-season camp in Austria.