An override template for ECP 4.0 week view tooltip display. It will strip HTML from the tooltip.

tooltip.php

<?php

// Place in {your-theme}/tribe-events/pro/week/tooltip.php

/**
 *
 * Please see single-event.php in this directory for detailed instructions on how to use and modify these templates.
 *
 */

?>

<script type="text/html" id="tribe_tmpl_tooltip">
	<div id="tribe-events-tooltip-[[=eventId]]" class="tribe-events-tooltip">
		<h4 class="tribe-event-title">[[=title]]</h4>

		<div class="tribe-events-event-body">
			<div class="tribe-event-duration">
				<abbr class="tribe-events-abbr tribe-event-date-start">[[=dateDisplay]] </abbr>
			</div>
			[[ if(imageTooltipSrc.length) { ]]
			<div class="tribe-events-event-thumb">
				<img src="[[=imageTooltipSrc]]" alt="[[=title]]" />
			</div>
			[[ } ]]
			[[ if(excerpt.length) { ]]
			<p class="tribe-event-description">[[=raw jQuery(excerpt).text()]]</p>
			[[ } ]]
			<span class="tribe-events-arrow"></span>
		</div>
	</div>
</script>