The Tottenham Hotspur hitman seemed to struggle on Merseyside.
Kane, who won the Premier League's Golden Boot last season, started up front in Saturday's 1-1 draw away to Everton but the 23-year-old striker had minimal impact in what has a very ordinary performance from the English hitman.
Tottenham improved quite a bit when Janssen - a £17 million signing from AZ Alkmaar - came on for Eric Dier in the 56th minute, and forced Maarten Stekelenburg into a fine save as he was denied a debut goal in Spurs colours.
Still, the 22-year-old looked a breath of fresh air at times for the Lilywhites at the weekend, and Shearer feels he can help out Kane when the latter is "anonymous" like he was at Goodison Park.
“He brought on Janssen to give Tottenham a little bit of help [up front]. Harry Kane was anonymous,” Shearer told BBC's Match of the Day program.
“For the first time, they started asking questions of Everton’s back five. Janssen took pressure of Kane, who wasn’t fighting five defenders like he was in the first half.”
Kane was poor, but Spurs fans won't be concerned just yet. It took him eight or nine games to warm up last term in a goal-laden season which yielded the Golden Boot, and few would write off his chances of winning it again.
Tottenham arguably suffered last time around as a result of no viable competition or alternatives to Kane, but if Janssen can become that figure then it would go a long way to seeing the North Londoners kick on this season.