Pienaar meanwhile, will miss out after he went off in the second half of the victory over Scarlets last weekend with a shoulder problem but Bell does not expect the South Africa scrum-half to be out of action for long.
"We would prefer that Ruan wasn't injured, but we have to manage him and hopefully he will be ready for next week - in a worst-case scenario to face Saracens after that," Bell told the Irish Independent.
"The players that come back will have to realise that this is a very crucial period for us. There is a lot at stake over the next few weeks, but having worked for Joe Schmidt in recent weeks, they know that they cannot take the foot of the gas."
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