It won't open any floodgates. The fact that team colleagues are observing that another colleague has changed their work pattern (whether temporarily or permanently - it doesn't matter which) does not create any automatic obligation to offer the same or similar. People already have the right - assuming requisite service length (soon not even that) - to make a flexible working request and the employer has an obligation to consider it and choose to agree, or alternatively decline it, assuming they have given it due consideration and the reason to decline is at least for one of the 8 fair business reasons). As an aside, if people are making approaches indicating increased levels of stress then that's a flag for the organisation to be considering what those stressors are, why they are there and what mitigations could or should be put in place. Going back to the original point though, the reason for the temporary working arrangement for the specific employee is situation - specific (ie they have been ill, and following medical advice, are returning on a phased return basis to enable them to return to work safely and build back up to 'normal' time and duties). Your other employees aren't necessarily party to this information (nor would they be, unless the employee themself has chosen to share it with them), so as is the way sometimes, they may see this as a disparity or 'unfair' to them (ie - 'I want what he's got') - if that's the case, then signpost them to the flex working provisions and treat each request as it comes, on its merits and in line with both the statutory requirements, and your organisational needs.