3 to 4 days should not be an issue but you have to be careful if they exceed certain number in a calendar year.
Please check Tier 2 guidance - page 116
https://www.gov.uk/government/publicati ... -employers.
26.25 You must not continue to sponsor a migrant who is absent from work without pay for 4 weeks or more in total, other than for the reasons listed above. You must report this using your SMS account. This applies whether the migrant is absent from work over a single period or more than one period during any calendar year (1 January to 31 December). The 4 weeks is worked out according to the migrant’s normal working pattern.
An example of this is if the migrant works 3 days per week (3 days x 4 weeks), it would be 12 working days.