Fire crews and police attended the fast food restaurant in Battlefield Road after it closed early at 9pm on Friday night.
The incident occurred at the same time armed officers – and a police helicopter – were on the other side of Shrewsbury looking for a man with a knife.
West Mercia Police described the incident at McDonald’s as “isolated and contained”, confirming it was not relating to the other incident.
A spokesperson for the fast food giant said on Saturday: “Last night a small number of our people complained of feeling unwell. The restaurant was closed as a precaution so that the fire brigade and our external service company could carry out an investigation.
“No evidence of any issues or contaminants were found within or around the restaurant.
“The store has been given a deep clean and reopened this morning.”
Reports had suggested a possible carbon monoxide leak, however the spokesperson said a thorough investigation had taken place looking at the refrigeration and air-conditioning systems had found no sign of any leakage.
While the reason for the staff feeling unwell has not been confirmed, restaurant managers felt confident to reopened the branch as usual on Saturday, and all members of staff are feeling better.