Gallinagh, who has played a bit-part role since late November and was an unused substitute in Saturday`s 1-0 win at Port Vale, will undergo a double hernia operation on Tuesday and be missing for around four weeks.
But manager Mark Yates has received some good news regarding another of his central defenders in Martin Riley, who is set to return to training on Tuesday after a hamstring injury.
The visit of Lincoln is likely to come too soon for Riley and he stands a better chance of being involved in Saturday`s trip to Oxford.
The Robins made three changes at Vale Park from the team beaten by Accrington a week earlier, and assistant manager Neil Howarth said: "It's all about the squad and not just about the 11 on the field.
"We decided to shuffle the pack for various reasons and the lads who came in all did well. Competition for places is healthy at any club."
Source: PA
Source: PA