Whittle (hamstring) was substituted at half-time against Bradford Park Avenue on January 4 and subsequently missed the home fixture against Curzon Ashton three days later while Thanoj (groin) has not featured since December 1 at Rochdale.
Manager Craig Elliott is hopeful of having the duo back in contention for Saturday's trip to the Pure Stadium (kick-off 3.00pm).
Striker Jake Wright will miss out with a shoulder injury.
United are currently four places and one point above the Sandgrounders, whom they defeated 2-0 at The Jakemans Stadium earlier in the campaign.
Last season's corresponding fixture ended 3-2 to the Pilgrims, with Nicky Walker scoring an 89th minute winner.
Saturday's match referee is Aaron Bannister, who last took charge of the Pilgrims on the opening day of the season against Chester FC.
POSTCODE FOR SAT NAV: PR8 6JZ.
BUSA COACH DEPARTURE: 9.30am.
UNITED COLOURS: Sky Blue.
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