Celtic lost to Lincoln Red Imps in Brendan Rodgers' first competitive match in charge.
Rodgers has made an inauspicious start at Celtic, after losing his first competitive match in charge to part time side Lincoln Red Imps in Champions League qualification.
The Imps beat Celtic 1-0, and the result will go down as one of the most embarrassing in the Glasgow side’s history.
Walker says that Celtic must use the loss as a wake up call, and hand Rodgers some money to spend now.
"I'm sure Brendan Rogders will realise that - he has to spend a bit of money. There's no point bringing in a manager of his pedigree and not giving him any money to work with in the transfer market,” Walker said.
When Rodgers took over at Celtic, there was a promise that he would have more money to spend than his predecessor, Ronny Deila.
However, Celtic’s progress in the transfer market has been slow so far.
The Bhoys have only managed to sign Moussa Dembele from Fulham, with a number of their transfer bids being turned down.
Rodgers has insisted this week that he is confident Celtic will get business done in the coming weeks.
Celtic are next in action on Saturday against Wolfsburg, before taking on the Imps again on Wednesday.