Vaughan twisted the same knee he hurt in a freak accident in the nets before the series against New Zealand when he missed the first Test last year, said England's media manager Andrew Walpole.
Vaughan, who had yet to score, suffered the injury on Monday while going for a run and fell to the ground in pain. He walked off the ground to get treatment.
"Vaughan has four to five days before the Test and it's early to say anything final but he was getting treatment," said Walpole.
Vaughan came into the second tour match needing some batting practice. He managed just nine and nought in the first tour match at Rawalpindi last week and 17 in the first innings of the current match.
SCOREBOARD
ENGLAND (1st innings): 126
(Mohammad Asif 7-62):
PAKISTAN 'A' (1st inning):
(overnight 127-8):
========================================
Imran Farhat lbw b Hoggard 23
Taufeeq Umar b Hoggard 6
Faisal Athar c Jones b Hoggard 0
Shahid Yousuf b Hoggard 10
Hasan Raza lbw b Giles 34
Mansoor Amjad b Collingwood 7
Amin-ur-Rehman c Flintoff b Giles 32
Arshad Khan lbw b Giles 0
Shahid Nazir not out 11
M.Asif c Trescothick b Harmison 6
Mohammad Khalil lbw b Harmison 1
Extras: (B-4, NB-4) 8
TOTAL: 138
========================================
FALL OF WICKETS: 1-9, 2-9, 3-29, 4-46, 5-58, 6-118, 7-118, 8-124, 9-132
BOWLING: Hoggard 8-0-39-4, Harmison 10.5-0-54-2, Collingwood 4-0-14-1, Flintoff 7-2-13-0, Giles 4-1-14-3.
OVERS: 33.5
ENGLAND (2ND INNINGS):
========================================
M. Trescothick lbw b Asif 1
A. Strauss c Rehman b Nazir 56
M. Vaughan retired hurt 0
K. Pietersen lbw b Asif 0
P. Collingwood c Nazir b Amjad 61
A. Flintoff c Nazir b Amjad 28
G. Jones c Rehman b Amjad 30
A. Giles c Nazir b Asif 49
S. Udal c Ather b Amjad 12
M. Hoggard b Amjad 3
S. Harmison not out 9
EXTRAS: (B-4, LB-1, W-2) 7
TOTAL: 256
========================================
FALL OF WICKETS: 1-4, 2-10, 3-123, 4-124, 5-154, 6-212, 7-226, 8-230, 9-256
BOWLING: Nazir 11-2-55-1, Asif 11.4-2-44-3, Khan 17-2-55-0, Amjad 24-3-97-5
OVERS: 63.4
PAKISTAN 'A' (2ND INNINGS):
========================================
Imran Farhat not out 12
Taufiq Umer c Jones b Hoggard 15
Shahid Nazir not out 0
EXTRAS: (LB-4) 4
TOTAL: (for 1 wkt) 31
========================================
FALL OF WICKETS: 1-27
BOWLING: Hoggard 2-0-22-0, Harmison 2-1-5-0
OVERS: 4
UMPIRES: Mian Mohammad Aslam and Salim Badar.