Both players have missed the majority of the season but will pair up at centre following their recoveries from knee problems.
Tuilagi damaged the meniscus in his knee in September in his first game back after eight months out, while Toomua has been sidelined by bruising.
The return of the duo will come as a boost to Leicester, who sit bottom of Pool 4 at the midway point in the group.
“Matt and Manu have been training hard, they’re world-class operators and it’s great to have them back,” said head coach Matt O’Connor.
“We prepared well for last weekend [a 33-10 defeat to pool leaders Munster] but we didn’t deliver on the day and were beaten by a very committed Munster side.
“Now we are looking at a big reaction at home this week. Pool 4 is the tightest of all the groups in the competition and all four teams still have everything to play for.”
— Leicester Tigers (@LeicesterTigers) December 15, 2017
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