Waghorn sustained the problem during England Under-21s' 3-0 win over Iceland last week and returned to the Tigers to undergo treatment.
And although the injury is not as bad as first feared, the 21-year-old is struggling for the Amex Stadium clash.
"We assessed Martyn on Friday and gave him treatment over the weekend and he's responded really well to that," head of medical services Chris Burton told the club's official website.
"He's been in the gym and doing a rehab programme and we'll progress him as soon as we can.
"He is a doubt for the Brighton game and we're probably looking more towards the Watford game, but we will assess that and see how he's doing towards the end of the week."